diff --git a/accessible/tests/browser/e10s/browser_caching_name.js b/accessible/tests/browser/e10s/browser_caching_name.js
index 08e635014408..9a5fd3e26d5b 100644
--- a/accessible/tests/browser/e10s/browser_caching_name.js
+++ b/accessible/tests/browser/e10s/browser_caching_name.js
@@ -392,7 +392,7 @@ function* testSubtreeRule(browser, target, rule, expected) {
   yield ContentTask.spawn(browser, target.id, id => {
     let elm = content.document.getElementById(id);
     while (elm.firstChild) {
-      elm.removeChild(elm.firstChild);
+      elm.firstChild.remove();
     }
   });
   yield updateAccessibleIfNeeded(onEvent, target);
diff --git a/accessible/tests/browser/e10s/browser_treeupdate_doc.js b/accessible/tests/browser/e10s/browser_treeupdate_doc.js
index ccb1d15668a1..73c6539e52c2 100644
--- a/accessible/tests/browser/e10s/browser_treeupdate_doc.js
+++ b/accessible/tests/browser/e10s/browser_treeupdate_doc.js
@@ -157,7 +157,7 @@ addAccessibleTask(`
   yield ContentTask.spawn(browser, {}, () => {
     // Remove HTML element.
     let docNode = content.document.getElementById('iframe').contentDocument;
-    docNode.removeChild(docNode.firstChild);
+    docNode.firstChild.remove();
   });
   let event = yield reorderEventPromise;
 
@@ -235,7 +235,7 @@ addAccessibleTask(`
     let docEl =
       content.document.getElementById('iframe').contentDocument.documentElement;
     // Remove aftermath of this test before next test starts.
-    docEl.removeChild(docEl.firstChild);
+    docEl.firstChild.remove();
   });
   // Make sure reorder event was fired and that the input was removed.
   yield reorderEventPromise;
diff --git a/accessible/tests/browser/e10s/browser_treeupdate_optgroup.js b/accessible/tests/browser/e10s/browser_treeupdate_optgroup.js
index 45001afaac34..18953380dcc0 100644
--- a/accessible/tests/browser/e10s/browser_treeupdate_optgroup.js
+++ b/accessible/tests/browser/e10s/browser_treeupdate_optgroup.js
@@ -56,7 +56,7 @@ addAccessibleTask('<select id="select"></select>', function*(browser, accDoc) {
   // Remove grouping from combobox
   yield ContentTask.spawn(browser, {}, () => {
     let contentSelect = content.document.getElementById('select');
-    contentSelect.removeChild(contentSelect.firstChild);
+    contentSelect.firstChild.remove();
   });
   yield onEvent;
 
diff --git a/accessible/tests/mochitest/events/test_mutation.html b/accessible/tests/mochitest/events/test_mutation.html
index 3e7dab6d46ac..4c9b8f33306a 100644
--- a/accessible/tests/mochitest/events/test_mutation.html
+++ b/accessible/tests/mochitest/events/test_mutation.html
@@ -414,8 +414,8 @@
         var l1 = doc.firstChild;
         this.target = l1.firstChild;
         var l2 = doc.lastChild;
-        l1.DOMNode.removeChild(l1.DOMNode.firstChild);
-        l2.DOMNode.removeChild(l2.DOMNode.firstChild);
+        l1.DOMNode.firstChild.remove();
+        l2.DOMNode.firstChild.remove();
       }
 
       this.check = function hideHideNDestroyDoc_check()
diff --git a/accessible/tests/mochitest/events/test_text.html b/accessible/tests/mochitest/events/test_text.html
index d992d6c641df..76dd1ce49af0 100644
--- a/accessible/tests/mochitest/events/test_text.html
+++ b/accessible/tests/mochitest/events/test_text.html
@@ -51,7 +51,7 @@
       this.invoke = function removeChildSpan_invoke()
       {
         // remove HTML span, a first child of the node
-        this.DOMNode.removeChild(this.DOMNode.firstChild);
+        this.DOMNode.firstChild.remove();
       }
 
       this.getID = function removeChildSpan_getID()
@@ -162,7 +162,7 @@
             this.DOMNode.removeChild(this.DOMNode.lastChild);
         } else {
           while (this.DOMNode.firstChild)
-            this.DOMNode.removeChild(this.DOMNode.firstChild);
+            this.DOMNode.firstChild.remove();
         }
       }
 
diff --git a/accessible/tests/mochitest/name/markup.js b/accessible/tests/mochitest/name/markup.js
index d3ecd8982b08..9d1c09562ed0 100644
--- a/accessible/tests/mochitest/name/markup.js
+++ b/accessible/tests/mochitest/name/markup.js
@@ -316,7 +316,7 @@ function testNameForSubtreeRule(aElm, aRule)
   waitForEvent(EVENT_REORDER, aElm, gTestIterator.iterateNext, gTestIterator);
 
   while (aElm.firstChild)
-    aElm.removeChild(aElm.firstChild);
+    aElm.firstChild.remove();
 }
 
 /**
diff --git a/accessible/tests/mochitest/treeupdate/test_doc.html b/accessible/tests/mochitest/treeupdate/test_doc.html
index 05896e7b46fa..3d108b0359dc 100644
--- a/accessible/tests/mochitest/treeupdate/test_doc.html
+++ b/accessible/tests/mochitest/treeupdate/test_doc.html
@@ -266,7 +266,7 @@
 
         // Remove HTML element.
         var docNode = getDocNode(aID);
-        docNode.removeChild(docNode.firstChild);
+        docNode.firstChild.remove();
       }
 
       this.getID = function removeHTMLFromIFrameDoc_getID()
diff --git a/accessible/tests/mochitest/treeupdate/test_general.html b/accessible/tests/mochitest/treeupdate/test_general.html
index 9a8862bea167..64ebdb52412f 100644
--- a/accessible/tests/mochitest/treeupdate/test_general.html
+++ b/accessible/tests/mochitest/treeupdate/test_general.html
@@ -64,7 +64,7 @@
 
       this.invoke = function removeRemove_invoke()
       {
-        getNode(aContainer).removeChild(getNode(aContainer).firstChild);
+        getNode(aContainer).firstChild.remove();
       }
 
       this.finalCheck = function removeRemove_finalCheck()
diff --git a/accessible/tests/mochitest/treeupdate/test_optgroup.html b/accessible/tests/mochitest/treeupdate/test_optgroup.html
index 27323bbc38da..22495c8e9273 100644
--- a/accessible/tests/mochitest/treeupdate/test_optgroup.html
+++ b/accessible/tests/mochitest/treeupdate/test_optgroup.html
@@ -77,7 +77,7 @@
       this.invoke = function removeOptGroup_invoke()
       {
         this.option1Node = this.selectNode.firstChild.firstChild;
-        this.selectNode.removeChild(this.selectNode.firstChild);
+        this.selectNode.firstChild.remove();
       }
 
       this.eventSeq = [
diff --git a/browser/base/content/browser-ctrlTab.js b/browser/base/content/browser-ctrlTab.js
index df51349edb19..3e69c3b442fb 100644
--- a/browser/base/content/browser-ctrlTab.js
+++ b/browser/base/content/browser-ctrlTab.js
@@ -241,7 +241,7 @@ var ctrlTab = {
     aPreview._tab = aTab;
 
     if (aPreview.firstChild)
-      aPreview.removeChild(aPreview.firstChild);
+      aPreview.firstChild.remove();
     if (aTab) {
       let canvasWidth = this.canvasWidth;
       let canvasHeight = this.canvasHeight;
diff --git a/browser/base/content/browser-fxaccounts.js b/browser/base/content/browser-fxaccounts.js
index 77f5e898ecda..7c6b16ab5456 100644
--- a/browser/base/content/browser-fxaccounts.js
+++ b/browser/base/content/browser-fxaccounts.js
@@ -330,7 +330,7 @@ var gFxAccounts = {
   populateSendTabToDevicesMenu(devicesPopup, url, title) {
     // remove existing menu items
     while (devicesPopup.hasChildNodes()) {
-      devicesPopup.removeChild(devicesPopup.firstChild);
+      devicesPopup.firstChild.remove();
     }
 
     const fragment = document.createDocumentFragment();
diff --git a/browser/base/content/browser-places.js b/browser/base/content/browser-places.js
index 372d107c5cf8..16dfd6d0d081 100644
--- a/browser/base/content/browser-places.js
+++ b/browser/base/content/browser-places.js
@@ -746,7 +746,7 @@ HistoryMenu.prototype = {
 
     // remove existing menu items
     while (undoPopup.hasChildNodes())
-      undoPopup.removeChild(undoPopup.firstChild);
+      undoPopup.firstChild.remove();
 
     // no restorable tabs, so make sure menu is disabled, and return
     if (this._getClosedTabCount() == 0) {
@@ -782,7 +782,7 @@ HistoryMenu.prototype = {
 
     // remove existing menu items
     while (undoPopup.hasChildNodes())
-      undoPopup.removeChild(undoPopup.firstChild);
+      undoPopup.firstChild.remove();
 
     // no restorable windows, so make sure menu is disabled, and return
     if (SessionStore.getClosedWindowCount() == 0) {
diff --git a/browser/base/content/pageinfo/pageInfo.js b/browser/base/content/pageinfo/pageInfo.js
index 98b12358beab..fca9da232b05 100644
--- a/browser/base/content/pageinfo/pageInfo.js
+++ b/browser/base/content/pageinfo/pageInfo.js
@@ -418,7 +418,7 @@ function resetPageInfo(args) {
   /* Reset Feeds Tab */
   var feedListbox = document.getElementById("feedListbox");
   while (feedListbox.firstChild)
-    feedListbox.removeChild(feedListbox.firstChild);
+    feedListbox.firstChild.remove();
 
   /* Call registered overlay reset functions */
   onResetRegistry.forEach(function(func) { func(); });
diff --git a/browser/base/content/pageinfo/security.js b/browser/base/content/pageinfo/security.js
index 6daf61d14e03..507b477bed75 100644
--- a/browser/base/content/pageinfo/security.js
+++ b/browser/base/content/pageinfo/security.js
@@ -306,7 +306,7 @@ function setText(id, value) {
     element.value = value;
   else {
     if (element.hasChildNodes())
-      element.removeChild(element.firstChild);
+      element.firstChild.remove();
     var textNode = document.createTextNode(value);
     element.appendChild(textNode);
   }
diff --git a/browser/base/content/utilityOverlay.js b/browser/base/content/utilityOverlay.js
index 94c1c98b0db8..9d37b9b816bb 100644
--- a/browser/base/content/utilityOverlay.js
+++ b/browser/base/content/utilityOverlay.js
@@ -490,7 +490,7 @@ function createUserContextMenu(event, {
                                         useAccessKeys = true
                                       } = {}) {
   while (event.target.hasChildNodes()) {
-    event.target.removeChild(event.target.firstChild);
+    event.target.firstChild.remove();
   }
 
   let bundle = document.getElementById("bundle_browser");
diff --git a/browser/components/customizableui/CustomizableWidgets.jsm b/browser/components/customizableui/CustomizableWidgets.jsm
index 36f659ae82d3..e2959dbd7fe7 100644
--- a/browser/components/customizableui/CustomizableWidgets.jsm
+++ b/browser/components/customizableui/CustomizableWidgets.jsm
@@ -244,12 +244,12 @@ const CustomizableWidgets = [
 
       let recentlyClosedTabs = doc.getElementById("PanelUI-recentlyClosedTabs");
       while (recentlyClosedTabs.firstChild) {
-        recentlyClosedTabs.removeChild(recentlyClosedTabs.firstChild);
+        recentlyClosedTabs.firstChild.remove();
       }
 
       let recentlyClosedWindows = doc.getElementById("PanelUI-recentlyClosedWindows");
       while (recentlyClosedWindows.firstChild) {
-        recentlyClosedWindows.removeChild(recentlyClosedWindows.firstChild);
+        recentlyClosedWindows.firstChild.remove();
       }
 
       let utils = RecentlyClosedTabsAndWindowsMenuUtils;
diff --git a/browser/components/customizableui/content/panelUI.js b/browser/components/customizableui/content/panelUI.js
index 6b29f3eee2fc..2ecddcbd7789 100644
--- a/browser/components/customizableui/content/panelUI.js
+++ b/browser/components/customizableui/content/panelUI.js
@@ -492,7 +492,7 @@ const PanelUI = {
 
     // Remove all buttons from the view
     while (items.firstChild) {
-      items.removeChild(items.firstChild);
+      items.firstChild.remove();
     }
 
     // Add the current set of menuitems of the Help menu to this view
diff --git a/browser/components/feeds/FeedWriter.js b/browser/components/feeds/FeedWriter.js
index a99bc4178d18..d82901e4aeb3 100644
--- a/browser/components/feeds/FeedWriter.js
+++ b/browser/components/feeds/FeedWriter.js
@@ -173,7 +173,7 @@ FeedWriter.prototype = {
     let element = this._document.getElementById(id);
     let textNode = text.createDocumentFragment(element);
     while (element.hasChildNodes())
-      element.removeChild(element.firstChild);
+      element.firstChild.remove();
     element.appendChild(textNode);
     if (text.base) {
       element.setAttributeNS(XML_NS, "base", text.base.spec);
diff --git a/browser/components/migration/content/migration.js b/browser/components/migration/content/migration.js
index c5d485f12579..87b229a444ca 100644
--- a/browser/components/migration/content/migration.js
+++ b/browser/components/migration/content/migration.js
@@ -185,7 +185,7 @@ var MigrationWizard = { /* exported MigrationWizard */
 
     var profiles = document.getElementById("profiles");
     while (profiles.hasChildNodes())
-      profiles.removeChild(profiles.firstChild);
+      profiles.firstChild.remove();
 
     // Note that this block is still reached even if the user chose 'From File'
     // and we canceled the dialog.  When that happens, _migrator will be null.
@@ -225,7 +225,7 @@ var MigrationWizard = { /* exported MigrationWizard */
   onImportItemsPageShow() {
     var dataSources = document.getElementById("dataSources");
     while (dataSources.hasChildNodes())
-      dataSources.removeChild(dataSources.firstChild);
+      dataSources.firstChild.remove();
 
     var items = this._migrator.getMigrateData(this._selectedProfile, this._autoMigrate);
     for (var i = 0; i < 16; ++i) {
@@ -367,7 +367,7 @@ var MigrationWizard = { /* exported MigrationWizard */
   _listItems(aID) {
     var items = document.getElementById(aID);
     while (items.hasChildNodes())
-      items.removeChild(items.firstChild);
+      items.firstChild.remove();
 
     var itemID;
     for (var i = 0; i < 16; ++i) {
diff --git a/browser/components/places/content/browserPlacesViews.js b/browser/components/places/content/browserPlacesViews.js
index 1a40b334bceb..7dea0891dcd8 100644
--- a/browser/components/places/content/browserPlacesViews.js
+++ b/browser/components/places/content/browserPlacesViews.js
@@ -1011,7 +1011,7 @@ PlacesToolbar.prototype = {
 
     this._openedMenuButton = null;
     while (this._rootElt.hasChildNodes()) {
-      this._rootElt.removeChild(this._rootElt.firstChild);
+      this._rootElt.firstChild.remove();
     }
 
     let cc = this._resultNode.childCount;
@@ -1952,7 +1952,7 @@ PlacesPanelMenuView.prototype = {
 
     // Container is the toolbar itself.
     while (this._rootElt.hasChildNodes()) {
-      this._rootElt.removeChild(this._rootElt.firstChild);
+      this._rootElt.firstChild.remove();
     }
 
     for (let i = 0; i < this._resultNode.childCount; ++i) {
diff --git a/browser/components/places/content/places.js b/browser/components/places/content/places.js
index 0ec3ef7531dd..bb97ea1c63fd 100644
--- a/browser/components/places/content/places.js
+++ b/browser/components/places/content/places.js
@@ -419,7 +419,7 @@ var PlacesOrganizer = {
 
     // Remove existing menu items.  Last item is the restoreFromFile item.
     while (restorePopup.childNodes.length > 1)
-      restorePopup.removeChild(restorePopup.firstChild);
+      restorePopup.firstChild.remove();
 
     Task.spawn(function* () {
       let backupFiles = yield PlacesBackups.getBackupFiles();
@@ -1007,7 +1007,7 @@ var ViewMenu = {
       return endElement;
     }
     while (popup.hasChildNodes()) {
-      popup.removeChild(popup.firstChild);
+      popup.firstChild.remove();
     }
     return null;
   },
diff --git a/browser/components/preferences/blocklists.js b/browser/components/preferences/blocklists.js
index c90d7ae5b773..c924133fd549 100644
--- a/browser/components/preferences/blocklists.js
+++ b/browser/components/preferences/blocklists.js
@@ -81,7 +81,7 @@ var gBlocklistManager = {
 
     let blocklistsText = document.getElementById("blocklistsText");
     while (blocklistsText.hasChildNodes()) {
-      blocklistsText.removeChild(blocklistsText.firstChild);
+      blocklistsText.firstChild.remove();
     }
     blocklistsText.appendChild(document.createTextNode(params.introText));
 
diff --git a/browser/components/preferences/in-content/advanced.js b/browser/components/preferences/in-content/advanced.js
index fc345f8f60d4..3f23def56226 100644
--- a/browser/components/preferences/in-content/advanced.js
+++ b/browser/components/preferences/in-content/advanced.js
@@ -557,7 +557,7 @@ var gAdvancedPane = {
 
     var list = document.getElementById("offlineAppsList");
     while (list.firstChild) {
-      list.removeChild(list.firstChild);
+      list.firstChild.remove();
     }
 
     var groups;
diff --git a/browser/components/preferences/languages.js b/browser/components/preferences/languages.js
index 6ad9bb13673e..e107a252a139 100644
--- a/browser/components/preferences/languages.js
+++ b/browser/components/preferences/languages.js
@@ -97,7 +97,7 @@ var gLanguagesDialog = {
   _buildAvailableLanguageList() {
     var availableLanguagesPopup = document.getElementById("availableLanguagesPopup");
     while (availableLanguagesPopup.hasChildNodes())
-      availableLanguagesPopup.removeChild(availableLanguagesPopup.firstChild);
+      availableLanguagesPopup.firstChild.remove();
 
     // Sort the list of languages by name
     this._availableLanguagesList.sort(function(a, b) {
@@ -119,7 +119,7 @@ var gLanguagesDialog = {
 
   readAcceptLanguages() {
     while (this._activeLanguages.hasChildNodes())
-      this._activeLanguages.removeChild(this._activeLanguages.firstChild);
+      this._activeLanguages.firstChild.remove();
 
     var selectedIndex = 0;
     var preference = document.getElementById("intl.accept_languages");
diff --git a/browser/components/preferences/permissions.js b/browser/components/preferences/permissions.js
index 1e188afcd23d..416d07e0bd57 100644
--- a/browser/components/preferences/permissions.js
+++ b/browser/components/preferences/permissions.js
@@ -218,7 +218,7 @@ var gPermissionManager = {
 
     var permissionsText = document.getElementById("permissionsText");
     while (permissionsText.hasChildNodes())
-      permissionsText.removeChild(permissionsText.firstChild);
+      permissionsText.firstChild.remove();
     permissionsText.appendChild(document.createTextNode(aParams.introText));
 
     document.title = aParams.windowTitle;
diff --git a/browser/components/syncedtabs/SyncedTabsDeckView.js b/browser/components/syncedtabs/SyncedTabsDeckView.js
index 4a31080297b5..8962e7b1854b 100644
--- a/browser/components/syncedtabs/SyncedTabsDeckView.js
+++ b/browser/components/syncedtabs/SyncedTabsDeckView.js
@@ -100,7 +100,7 @@ SyncedTabsDeckView.prototype = {
 
   _clearChilden() {
     while (this.container.firstChild) {
-      this.container.removeChild(this.container.firstChild);
+      this.container.firstChild.remove();
     }
   },
 
diff --git a/browser/components/syncedtabs/TabListView.js b/browser/components/syncedtabs/TabListView.js
index a8d1ed9c66f6..fc68cd73dea1 100644
--- a/browser/components/syncedtabs/TabListView.js
+++ b/browser/components/syncedtabs/TabListView.js
@@ -169,7 +169,7 @@ TabListView.prototype = {
   _clearChilden(node) {
     let parent = node || this.container;
     while (parent.firstChild) {
-      parent.removeChild(parent.firstChild);
+      parent.firstChild.remove();
     }
   },
 
diff --git a/browser/components/uitour/UITour.jsm b/browser/components/uitour/UITour.jsm
index 4048ff1c490c..e1890a68c1bb 100644
--- a/browser/components/uitour/UITour.jsm
+++ b/browser/components/uitour/UITour.jsm
@@ -1236,7 +1236,7 @@ this.UITour = {
       // Remove all the children of the notice (rating container
       // and the flex).
       while (notice.firstChild) {
-        notice.removeChild(notice.firstChild);
+        notice.firstChild.remove();
       }
 
       // Make sure that we have a valid URL. If we haven't, do not open the engagement page.
diff --git a/browser/extensions/pdfjs/content/web/viewer.js b/browser/extensions/pdfjs/content/web/viewer.js
index 42182992db0b..765f52e6d530 100644
--- a/browser/extensions/pdfjs/content/web/viewer.js
+++ b/browser/extensions/pdfjs/content/web/viewer.js
@@ -3898,7 +3898,7 @@ var PDFAttachmentViewer = function PDFAttachmentViewerClosure() {
    this.attachments = null;
    var container = this.container;
    while (container.firstChild) {
-    container.removeChild(container.firstChild);
+    container.firstChild.remove();
    }
    if (!keepRenderedCapability) {
     this._renderedCapability = pdfjsLib.createPromiseCapability();
@@ -4598,7 +4598,7 @@ var PDFOutlineViewer = function PDFOutlineViewerClosure() {
    this.lastToggleIsShow = true;
    var container = this.container;
    while (container.firstChild) {
-    container.removeChild(container.firstChild);
+    container.firstChild.remove();
    }
   },
   _dispatchEvent: function PDFOutlineViewer_dispatchEvent(outlineCount) {
diff --git a/devtools/client/debugger/new/debugger.js b/devtools/client/debugger/new/debugger.js
index c6ed2a7bb1f6..dddc5a6af7ba 100644
--- a/devtools/client/debugger/new/debugger.js
+++ b/devtools/client/debugger/new/debugger.js
@@ -36082,7 +36082,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	
 	function removeChildren(e) {
 	  for (var count = e.childNodes.length; count > 0; --count)
-	    { e.removeChild(e.firstChild) }
+	    { e.firstChild.remove() }
 	  return e
 	}
 	
diff --git a/devtools/client/framework/sidebar.js b/devtools/client/framework/sidebar.js
index 7625edf891e8..f611c4dfba3d 100644
--- a/devtools/client/framework/sidebar.js
+++ b/devtools/client/framework/sidebar.js
@@ -576,7 +576,7 @@ ToolSidebar.prototype = {
     }
 
     while (this._tabbox.tabs && this._tabbox.tabs.hasChildNodes()) {
-      this._tabbox.tabs.removeChild(this._tabbox.tabs.firstChild);
+      this._tabbox.tabs.firstChild.remove();
     }
 
     if (this._currentTool && this._telemetry) {
diff --git a/devtools/client/inspector/markup/markup.js b/devtools/client/inspector/markup/markup.js
index 9d8201ff6f17..2c511e42fc6c 100644
--- a/devtools/client/inspector/markup/markup.js
+++ b/devtools/client/inspector/markup/markup.js
@@ -1604,7 +1604,7 @@ MarkupView.prototype = {
       // this container will do double duty as the container for the single
       // text child.
       while (container.children.firstChild) {
-        container.children.removeChild(container.children.firstChild);
+        container.children.firstChild.remove();
       }
 
       container.setInlineTextChild(container.node.inlineTextChild);
@@ -1616,7 +1616,7 @@ MarkupView.prototype = {
 
     if (!container.hasChildren) {
       while (container.children.firstChild) {
-        container.children.removeChild(container.children.firstChild);
+        container.children.firstChild.remove();
       }
       container.childrenDirty = false;
       container.setExpanded(false);
@@ -1659,7 +1659,7 @@ MarkupView.prototype = {
         }
 
         while (container.children.firstChild) {
-          container.children.removeChild(container.children.firstChild);
+          container.children.firstChild.remove();
         }
 
         if (!(children.hasFirst && children.hasLast)) {
diff --git a/devtools/client/scratchpad/scratchpad.js b/devtools/client/scratchpad/scratchpad.js
index 57256dd53771..6f2cc9a176d3 100644
--- a/devtools/client/scratchpad/scratchpad.js
+++ b/devtools/client/scratchpad/scratchpad.js
@@ -1367,7 +1367,7 @@ var Scratchpad = {
 
     recentFilesMenu.setAttribute("disabled", true);
     while (recentFilesPopup.hasChildNodes()) {
-      recentFilesPopup.removeChild(recentFilesPopup.firstChild);
+      recentFilesPopup.firstChild.remove();
     }
 
     if (filePaths.length > 0) {
diff --git a/devtools/client/shared/developer-toolbar.js b/devtools/client/shared/developer-toolbar.js
index db6fae81db93..d2dc161b34c5 100644
--- a/devtools/client/shared/developer-toolbar.js
+++ b/devtools/client/shared/developer-toolbar.js
@@ -1019,7 +1019,7 @@ OutputPanel.prototype._update = function () {
 
   // Empty this._div
   while (this._div.hasChildNodes()) {
-    this._div.removeChild(this._div.firstChild);
+    this._div.firstChild.remove();
   }
 
   if (this.displayedOutput.data != null) {
@@ -1030,7 +1030,7 @@ OutputPanel.prototype._update = function () {
       }
 
       while (this._div.hasChildNodes()) {
-        this._div.removeChild(this._div.firstChild);
+        this._div.firstChild.remove();
       }
 
       let links = node.querySelectorAll("*[href]");
diff --git a/devtools/client/shared/widgets/TableWidget.js b/devtools/client/shared/widgets/TableWidget.js
index e4c8ed7f263c..60784a9caaab 100644
--- a/devtools/client/shared/widgets/TableWidget.js
+++ b/devtools/client/shared/widgets/TableWidget.js
@@ -1554,7 +1554,7 @@ Cell.prototype = {
       this.label.removeAttribute("value");
 
       while (this.label.firstChild) {
-        this.label.removeChild(this.label.firstChild);
+        this.label.firstChild.remove();
       }
 
       this.label.appendChild(value);
diff --git a/devtools/client/shared/widgets/tooltip/Tooltip.js b/devtools/client/shared/widgets/tooltip/Tooltip.js
index 4bb3c52f01ae..5e013cbcae0a 100644
--- a/devtools/client/shared/widgets/tooltip/Tooltip.js
+++ b/devtools/client/shared/widgets/tooltip/Tooltip.js
@@ -201,7 +201,7 @@ Tooltip.prototype = {
    */
   empty: function () {
     while (this.panel.hasChildNodes()) {
-      this.panel.removeChild(this.panel.firstChild);
+      this.panel.firstChild.remove();
     }
   },
 
diff --git a/devtools/client/styleeditor/StyleEditorUI.jsm b/devtools/client/styleeditor/StyleEditorUI.jsm
index ad3cb992df20..e35c8ffca54f 100644
--- a/devtools/client/styleeditor/StyleEditorUI.jsm
+++ b/devtools/client/styleeditor/StyleEditorUI.jsm
@@ -865,7 +865,7 @@ StyleEditorUI.prototype = {
       let list = details.querySelector(".stylesheet-media-list");
 
       while (list.firstChild) {
-        list.removeChild(list.firstChild);
+        list.firstChild.remove();
       }
 
       let rules = editor.mediaRules;
diff --git a/devtools/shared/gcli/commands/csscoverage.js b/devtools/shared/gcli/commands/csscoverage.js
index 841cf4c7dff9..2c7516a67f2c 100644
--- a/devtools/shared/gcli/commands/csscoverage.js
+++ b/devtools/shared/gcli/commands/csscoverage.js
@@ -156,7 +156,7 @@ exports.items = [
         onback: () => {
           // The back button clears and hides .csscoverage-report
           while (host.hasChildNodes()) {
-            host.removeChild(host.firstChild);
+            host.firstChild.remove();
           }
           host.hidden = true;
         }
diff --git a/devtools/shared/gcli/source/lib/gcli/util/util.js b/devtools/shared/gcli/source/lib/gcli/util/util.js
index 065bf36c07db..650e84b8f1f6 100644
--- a/devtools/shared/gcli/source/lib/gcli/util/util.js
+++ b/devtools/shared/gcli/source/lib/gcli/util/util.js
@@ -388,7 +388,7 @@ exports.createElement = function(doc, tag) {
  */
 exports.clearElement = function(elem) {
   while (elem.hasChildNodes()) {
-    elem.removeChild(elem.firstChild);
+    elem.firstChild.remove();
   }
 };
 
diff --git a/docshell/test/chrome/bug303267.html b/docshell/test/chrome/bug303267.html
index 32b575eee8dc..98042e830b04 100644
--- a/docshell/test/chrome/bug303267.html
+++ b/docshell/test/chrome/bug303267.html
@@ -13,7 +13,7 @@ function showpageshowcount()
 	var div1 = document.getElementById("div1");
 	while (div1.firstChild)
 	{
-		div1.removeChild(div1.firstChild);
+		div1.firstChild.remove();
 	}
 	div1.appendChild(document.createTextNode(
 	  "pageshowcount: " + pageshowcount));
diff --git a/docshell/test/navigation/file_bug534178.html b/docshell/test/navigation/file_bug534178.html
index 8bcedb6fbabe..7e357945d34c 100644
--- a/docshell/test/navigation/file_bug534178.html
+++ b/docshell/test/navigation/file_bug534178.html
@@ -3,7 +3,7 @@
     <script>
     
       function testDone() {
-        document.body.removeChild(document.body.firstChild);
+        document.body.firstChild.remove();
         var isOK = false;
         try {
           isOK = history.previous != location;
diff --git a/docshell/test/test_bug570341.html b/docshell/test/test_bug570341.html
index d09afa4bd06a..47dea92f8e89 100644
--- a/docshell/test/test_bug570341.html
+++ b/docshell/test/test_bug570341.html
@@ -31,7 +31,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=570341
 
   function showSequence(node){
     while(node.firstChild) {
-      node.removeChild(node.firstChild);
+      node.firstChild.remove();
     }
     var sequence = [];
     for (var p in moments) {
diff --git a/dom/base/crashtests/771639.html b/dom/base/crashtests/771639.html
index d46fcba23e20..c6124cac51a9 100644
--- a/dom/base/crashtests/771639.html
+++ b/dom/base/crashtests/771639.html
@@ -1,7 +1,7 @@
 <!DOCTYPE html>
 <script>
 var root = document.documentElement;
-while(root.firstChild) { root.removeChild(root.firstChild); }
+while(root.firstChild) { root.firstChild.remove(); }
 var div = document.createElement("div");
 root.appendChild(div);
 
diff --git a/dom/base/test/test_bug416383.html b/dom/base/test/test_bug416383.html
index 741fbf878057..33bd65c882b6 100644
--- a/dom/base/test/test_bug416383.html
+++ b/dom/base/test/test_bug416383.html
@@ -26,7 +26,7 @@ function runTest() {
   ok(attrs != null, "Element should have attributes!");
   var attr = testParent.firstChild.getAttributeNode("someattr");
   ok(attr.value == "foo", "The value of the attribute should be 'foo'!");
-  testParent.removeChild(testParent.firstChild);
+  testParent.firstChild.remove();
   SpecialPowers.gc();
   ok(true, "Browser should not crash!")
 
diff --git a/dom/base/test/test_mutationobservers.html b/dom/base/test/test_mutationobservers.html
index bde07c79cb7a..f26de3728a63 100644
--- a/dom/base/test/test_mutationobservers.html
+++ b/dom/base/test/test_mutationobservers.html
@@ -246,7 +246,7 @@ function testChildList() {
       m = null;
     });
   m.observe(div, { childList: true});
-  div.removeChild(div.firstChild);
+  div.firstChild.remove();
 }
 
 function testChildList2() {
diff --git a/dom/html/crashtests/453406-1.html b/dom/html/crashtests/453406-1.html
index 2017f2b1af44..bf756865538c 100644
--- a/dom/html/crashtests/453406-1.html
+++ b/dom/html/crashtests/453406-1.html
@@ -5,7 +5,7 @@ function boom()
 {
   var r = document.documentElement;
   while (r.firstChild)
-    r.removeChild(r.firstChild);
+    r.firstChild.remove();
 
   var b    = document.createElement("BODY");
   var s    = document.createElement("SCRIPT");
diff --git a/dom/html/crashtests/564461.xhtml b/dom/html/crashtests/564461.xhtml
index 841058eb6c76..c92555a2e392 100644
--- a/dom/html/crashtests/564461.xhtml
+++ b/dom/html/crashtests/564461.xhtml
@@ -11,7 +11,7 @@
 
 function boom()
 {
-  while (document.documentElement.firstChild) document.documentElement.removeChild(document.documentElement.firstChild);
+  while (document.documentElement.firstChild) document.documentElement.firstChild.remove();
   
   document.addEventListener("DOMSubtreeModified", function(){});
   document.addEventListener("DOMNodeInsertedIntoDocument", function(){});
diff --git a/dom/html/test/forms/test_form_attribute-1.html b/dom/html/test/forms/test_form_attribute-1.html
index 34eda40bcbed..9d41d2331a13 100644
--- a/dom/html/test/forms/test_form_attribute-1.html
+++ b/dom/html/test/forms/test_form_attribute-1.html
@@ -424,7 +424,7 @@ for (var name of elementNames) {
   for (var func of functions) {
     // Clean-up.
     while (content.firstChild) {
-      content.removeChild(content.firstChild);
+      content.firstChild.remove();
     }
     for (form of forms) {
       content.appendChild(form);
diff --git a/dom/html/test/test_bug300691-1.html b/dom/html/test/test_bug300691-1.html
index 40d12f9bf65f..cce870cece12 100644
--- a/dom/html/test/test_bug300691-1.html
+++ b/dom/html/test/test_bug300691-1.html
@@ -95,7 +95,7 @@ valueIs("abcdeTesth",
         "Modifying textnode text shouldn't affect value in edited textarea");
 defValueIs("abcdefghlmno", "Modified textnode text 3");
 
-t.removeChild(t.firstChild);
+t.firstChild.remove();
 valueIs("abcdeTesth",
         "Removing child textnode shouldn't affect value in edited textarea");
 defValueIs("defghlmno", "Removed textnode 3");
diff --git a/dom/html/test/test_bug311681.html b/dom/html/test/test_bug311681.html
index 4f84d62a52f6..3199b22c26b9 100644
--- a/dom/html/test/test_bug311681.html
+++ b/dom/html/test/test_bug311681.html
@@ -78,7 +78,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=311681
 
   function clear(node) {
     while (node.hasChildNodes()) {
-      node.removeChild(node.firstChild);
+      node.firstChild.remove();
     }
   }
 
diff --git a/dom/html/test/test_bug311681.xhtml b/dom/html/test/test_bug311681.xhtml
index 78cada120bc1..6c334f796c72 100644
--- a/dom/html/test/test_bug311681.xhtml
+++ b/dom/html/test/test_bug311681.xhtml
@@ -78,7 +78,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=311681
 
   function clear(node) {
     while (node.hasChildNodes()) {
-      node.removeChild(node.firstChild);
+      node.firstChild.remove();
     }
   }
 
diff --git a/dom/html/test/test_bug691.html b/dom/html/test/test_bug691.html
index cfdb539852e2..0d5a8358cc6a 100644
--- a/dom/html/test/test_bug691.html
+++ b/dom/html/test/test_bug691.html
@@ -23,7 +23,7 @@ function remove() {
   var stage = document.getElementById("stage");
   var body = document.getElementsByTagName("BODY")[0];
   while (stage.firstChild) {
-    stage.removeChild(stage.firstChild);
+    stage.firstChild.remove();
   }
 }
 
diff --git a/dom/media/test/manifest.js b/dom/media/test/manifest.js
index bda391bc312b..5c2799648d4d 100644
--- a/dom/media/test/manifest.js
+++ b/dom/media/test/manifest.js
@@ -1545,7 +1545,7 @@ function removeNodeAndSource(n) {
   n.srcObject = null;
   n.src = "";
   while (n.firstChild) {
-    n.removeChild(n.firstChild);
+    n.firstChild.remove();
   }
 }
 
diff --git a/dom/media/webvtt/vtt.jsm b/dom/media/webvtt/vtt.jsm
index fb0d4867a97a..7837340b16ee 100644
--- a/dom/media/webvtt/vtt.jsm
+++ b/dom/media/webvtt/vtt.jsm
@@ -889,7 +889,7 @@ Cu.import('resource://gre/modules/Services.jsm');
 
     // Remove all previous children.
     while (overlay.firstChild) {
-      overlay.removeChild(overlay.firstChild);
+      overlay.firstChild.remove();
     }
 
     var controlBar;
diff --git a/dom/smil/test/test_smilChangeAfterFrozen.xhtml b/dom/smil/test/test_smilChangeAfterFrozen.xhtml
index 467c1a1d10a3..abf943de24f0 100644
--- a/dom/smil/test/test_smilChangeAfterFrozen.xhtml
+++ b/dom/smil/test/test_smilChangeAfterFrozen.xhtml
@@ -188,7 +188,7 @@ function testCurrentColorChange()
 
   // Clean up
   gCircle.removeAttribute("color");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testCurrentColorChangeUsingStyle()
@@ -209,7 +209,7 @@ function testCurrentColorChangeUsingStyle()
 
   // Clean up
   gCircle.removeAttribute("style");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function getFallbackColor(pServerStr)
@@ -236,7 +236,7 @@ function testCurrentColorChangeOnFallback()
      "Checking animated fallback fill=currentColor after updating context");
 
   gCircle.removeAttribute("style");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testInheritChange()
@@ -255,7 +255,7 @@ function testInheritChange()
      "Checking animated fill=inherit after updating context");
 
   gCircleParent.removeAttribute("fill");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testInheritChangeUsingStyle()
@@ -275,7 +275,7 @@ function testInheritChangeUsingStyle()
      + "(using style attr)");
 
   gCircleParent.removeAttribute("style");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testEmUnitChangeOnProp()
@@ -294,7 +294,7 @@ function testEmUnitChangeOnProp()
      "Checking animated font-size=2em after updating context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testEmUnitChangeOnPropBase()
@@ -319,7 +319,7 @@ function testEmUnitChangeOnPropBase()
      "Checking animated font-size=30px after updating context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testEmUnitChangeOnLength()
@@ -344,7 +344,7 @@ function testEmUnitChangeOnLength()
      "resampling");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testPercentUnitChangeOnProp()
@@ -363,7 +363,7 @@ function testPercentUnitChangeOnProp()
      "Checking animated font-size=150% after updating context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testPercentUnitChangeOnLength()
@@ -399,7 +399,7 @@ function testPercentUnitChangeOnLength()
      "Checking animated length=100% after updating context");
 
   gSvg.setAttribute("height", oldHeight);
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testRelativeFontSize()
@@ -421,7 +421,7 @@ function testRelativeFontSize()
   ok(fsize > 20, "Checking animated font-size > 20px after updating context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testRelativeFontWeight()
@@ -447,7 +447,7 @@ function testRelativeFontWeight()
      "Checking animated font-weight = 900 after updating context");
 
   gCircleParent.removeAttribute("font-weight");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testRelativeFont()
@@ -479,7 +479,7 @@ function testRelativeFont()
      "Checking size of shorthand 'font' > 20px after updating context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testCalcFontSize()
@@ -500,7 +500,7 @@ function testCalcFontSize()
                 "context");
 
   gCircleParent.removeAttribute("font-size");
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testDashArray()
@@ -529,7 +529,7 @@ function testDashArray()
 
   gSvg.setAttribute("height", oldHeight);
   gSvg.setAttribute("width",  oldWidth);
-  gCircle.removeChild(gCircle.firstChild);
+  gCircle.firstChild.remove();
 }
 
 function testClip()
diff --git a/dom/svg/test/test_SVGTransformListAddition.xhtml b/dom/svg/test/test_SVGTransformListAddition.xhtml
index 3f204192cff2..db43bf780ada 100644
--- a/dom/svg/test/test_SVGTransformListAddition.xhtml
+++ b/dom/svg/test/test_SVGTransformListAddition.xhtml
@@ -153,7 +153,7 @@ function runAdditionTestCase(test, elem, svg)
   // We assume the only children of elem are the animation elements we've just
   // added.
   while (elem.firstChild) {
-    elem.removeChild(elem.firstChild);
+    elem.firstChild.remove();
   }
 }
 
diff --git a/dom/svg/test/test_text_dirty.html b/dom/svg/test/test_text_dirty.html
index 7f17484e6b56..e7df5ef198a1 100644
--- a/dom/svg/test/test_text_dirty.html
+++ b/dom/svg/test/test_text_dirty.html
@@ -28,7 +28,7 @@ function runTest() {
 
   // Dirty the frames.
   document.getElementById("display").style.width = "700px";
-  svgText.removeChild(svgText.firstChild);
+  svgText.firstChild.remove();
 
   // Paint without flushing layout.  If the test fails, we'll trigger
   // an assertion.
diff --git a/dom/svg/test/test_text_update.html b/dom/svg/test/test_text_update.html
index cadb218a5fd4..d4677aaeacfc 100644
--- a/dom/svg/test/test_text_update.html
+++ b/dom/svg/test/test_text_update.html
@@ -25,7 +25,7 @@ ok(length > 0, "text.getComputedTextLength() > 0");
 text.firstChild.nodeValue += "cd";
 ok(text.getComputedTextLength() > length, "text.getComputedTextLength() changes directly after DOM mutation");
 
-text.removeChild(text.firstChild);
+text.firstChild.remove();
 is(text.getComputedTextLength(), 0, "text.getComputedTextLength() == 0 after removing child");
 </script>
 </pre>
diff --git a/dom/tests/mochitest/webcomponents/test_shadow_element.html b/dom/tests/mochitest/webcomponents/test_shadow_element.html
index 4440650d7d9b..4b91535fc325 100644
--- a/dom/tests/mochitest/webcomponents/test_shadow_element.html
+++ b/dom/tests/mochitest/webcomponents/test_shadow_element.html
@@ -90,7 +90,7 @@ ok(firstDistNodes[0].id == "one" &&
    firstDistNodes[3].id == "four", "Reprojection through shadow should preserve node order.");
 
 // Remove a node from the host and make sure that it is removed from all insertion points.
-host.removeChild(host.firstChild);
+host.firstChild.remove();
 firstDistNodes = firstContent.getDistributedNodes();
 secondDistNodes = secondContent.getDistributedNodes();
 
@@ -115,7 +115,7 @@ firstShadow.appendChild(shadowChild);
 is(firstContent.getDistributedNodes()[0], shadowChild, "Elements in shadow insertioin point should be projected into content insertion points.");
 
 // Remove child of ShadowRoot and check that projected node is removed from insertion point.
-firstShadow.removeChild(firstShadow.firstChild);
+firstShadow.firstChild.remove();
 
 is(firstContent.getDistributedNodes().length, 0, "Reprojected element was removed from ShadowRoot, thus it should be removed from content insertion point.");
 
@@ -135,7 +135,7 @@ host.innerHTML = '<span></span>';
 is(firstContent.getDistributedNodes()[0], host.firstChild, "Child of host should be projected to insertion point.");
 
 // Remove node and make sure that it is removed from distributed nodes.
-host.removeChild(host.firstChild);
+host.firstChild.remove();
 
 is(firstContent.getDistributedNodes().length, 0, "Node removed from host should be removed from insertion point.");
 
diff --git a/dom/xslt/tests/mochitest/test_bug319374.xhtml b/dom/xslt/tests/mochitest/test_bug319374.xhtml
index 2342b3447419..b752c5e4eed1 100644
--- a/dom/xslt/tests/mochitest/test_bug319374.xhtml
+++ b/dom/xslt/tests/mochitest/test_bug319374.xhtml
@@ -45,7 +45,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=319374
       while (res = result.iterateNext()) {
         ++counter; 
         var anon = getAnonymousNodes(res);
-        anon[0].removeChild(anon[0].firstChild); // Removing a child node
+        anon[0].firstChild.remove(); // Removing a child node
         anon[0].removeAttribute("attr1"); // Removing an attribute
         anon[1].firstChild.data = "anon text changed" // Modifying text data
       }
diff --git a/dom/xul/templates/tests/chrome/test_sortservice.xul b/dom/xul/templates/tests/chrome/test_sortservice.xul
index af1de3f0ef36..b7d5848a1148 100644
--- a/dom/xul/templates/tests/chrome/test_sortservice.xul
+++ b/dom/xul/templates/tests/chrome/test_sortservice.xul
@@ -56,7 +56,7 @@ function doTests()
     is(actual, test[2], "sorted step " + (t + 1));
 
     while(box.hasChildNodes())
-      box.removeChild(box.firstChild);
+      box.firstChild.remove();
     box.removeAttribute("sortDirection");
   }
 
diff --git a/dom/xul/test/test_bug311681.xul b/dom/xul/test/test_bug311681.xul
index 515bd67bf81d..9c22246c6268 100644
--- a/dom/xul/test/test_bug311681.xul
+++ b/dom/xul/test/test_bug311681.xul
@@ -81,7 +81,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=311681
 
   function clear(node) {
     while (node.hasChildNodes()) {
-      node.removeChild(node.firstChild);
+      node.firstChild.remove();
     }
   }
 
diff --git a/editor/composer/crashtests/407062-1.html b/editor/composer/crashtests/407062-1.html
index 81083c235d53..9bd5d02e59e7 100644
--- a/editor/composer/crashtests/407062-1.html
+++ b/editor/composer/crashtests/407062-1.html
@@ -7,7 +7,7 @@ function boom()
 {
   var r = document.documentElement;
   while(r.firstChild)
-    r.removeChild(r.firstChild);
+    r.firstChild.remove();
 
   document.execCommand("contentReadOnly", false, "");
   document.documentElement.focus();
diff --git a/editor/libeditor/crashtests/1317718.html b/editor/libeditor/crashtests/1317718.html
index ecef30e0d909..892b8aee3127 100644
--- a/editor/libeditor/crashtests/1317718.html
+++ b/editor/libeditor/crashtests/1317718.html
@@ -4,7 +4,7 @@
 addEventListener('DOMContentLoaded', function() {
   let root = document.documentElement;
   while(root.firstChild) {
-    root.removeChild(root.firstChild);
+    root.firstChild.remove();
   }
   document.designMode = 'on';
   document.removeChild(document.documentElement);
diff --git a/editor/libeditor/crashtests/1324505.html b/editor/libeditor/crashtests/1324505.html
index 2af15becc7c6..4872b9f05d99 100644
--- a/editor/libeditor/crashtests/1324505.html
+++ b/editor/libeditor/crashtests/1324505.html
@@ -4,7 +4,7 @@
 addEventListener("DOMContentLoaded", function(){
   let root = document.documentElement;
   while(root.firstChild) {
-    root.removeChild(root.firstChild);
+    root.firstChild.remove();
   }
   let o_0 = document.createElement("body");
   root.appendChild(o_0);
diff --git a/editor/libeditor/crashtests/612565-1.html b/editor/libeditor/crashtests/612565-1.html
index 1b059aa6624c..8df4283f8da9 100644
--- a/editor/libeditor/crashtests/612565-1.html
+++ b/editor/libeditor/crashtests/612565-1.html
@@ -10,7 +10,7 @@
       doc.body.appendChild(doc.createTextNode("foo"));
       doc.designMode = "on";
       while (doc.body.firstChild) {
-        doc.body.removeChild(doc.body.firstChild);
+        doc.body.firstChild.remove();
       }
     };
   </script>
diff --git a/editor/libeditor/crashtests/713427-2.xhtml b/editor/libeditor/crashtests/713427-2.xhtml
index 7ebfb7775af7..39ac18ed07e7 100644
--- a/editor/libeditor/crashtests/713427-2.xhtml
+++ b/editor/libeditor/crashtests/713427-2.xhtml
@@ -6,7 +6,7 @@
 function boom()
 {
   while (document.documentElement.firstChild) {
-    document.documentElement.removeChild(document.documentElement.firstChild);
+    document.documentElement.firstChild.remove();
   }
 
   var td = document.createElementNS("http://www.w3.org/1999/xhtml", "td");
diff --git a/editor/libeditor/crashtests/761861.html b/editor/libeditor/crashtests/761861.html
index 0c1f3f521056..2a7e06a15491 100644
--- a/editor/libeditor/crashtests/761861.html
+++ b/editor/libeditor/crashtests/761861.html
@@ -3,7 +3,7 @@
 function boom() {
   var r = document.documentElement;
   while (r.firstChild) {
-    r.removeChild(r.firstChild);
+    r.firstChild.remove();
   }
 
   document.documentElement.contentEditable = "true";
diff --git a/editor/libeditor/crashtests/766413.html b/editor/libeditor/crashtests/766413.html
index c5d9835e3ca7..1a7092d92a0a 100644
--- a/editor/libeditor/crashtests/766413.html
+++ b/editor/libeditor/crashtests/766413.html
@@ -7,7 +7,7 @@ function boom()
 {
   var root = document.documentElement;
   while (root.firstChild) {
-    root.removeChild(root.firstChild);
+    root.firstChild.remove();
   }
 
   var space = document.createTextNode(" ");
diff --git a/editor/libeditor/crashtests/767169.html b/editor/libeditor/crashtests/767169.html
index 3dfad160c1c6..a7673bce62bf 100644
--- a/editor/libeditor/crashtests/767169.html
+++ b/editor/libeditor/crashtests/767169.html
@@ -7,7 +7,7 @@
 function boom()
 {
   var root = document.documentElement;
-  while (root.firstChild) { root.removeChild(root.firstChild); }
+  while (root.firstChild) { root.firstChild.remove(); }
   root.contentEditable = "true";
   document.removeChild(root);
   document.appendChild(root);
diff --git a/editor/libeditor/crashtests/768765.html b/editor/libeditor/crashtests/768765.html
index 060e5161bd08..551e4ec6c380 100644
--- a/editor/libeditor/crashtests/768765.html
+++ b/editor/libeditor/crashtests/768765.html
@@ -7,7 +7,7 @@ function boom()
 {
   var root = document.documentElement;
 
-  while (root.firstChild) { root.removeChild(root.firstChild); }
+  while (root.firstChild) { root.firstChild.remove(); }
 
   var body = document.createElementNS("http://www.w3.org/1999/xhtml", "body");
   var div = document.createElementNS("http://www.w3.org/1999/xhtml", "div");
diff --git a/editor/libeditor/crashtests/772282.html b/editor/libeditor/crashtests/772282.html
index f6259b344cf7..bba3d6bd6733 100644
--- a/editor/libeditor/crashtests/772282.html
+++ b/editor/libeditor/crashtests/772282.html
@@ -6,7 +6,7 @@
 function boom()
 {
   var root = document.documentElement;
-  while(root.firstChild) { root.removeChild(root.firstChild); }
+  while(root.firstChild) { root.firstChild.remove(); }
   var body = document.createElementNS("http://www.w3.org/1999/xhtml", "body");
   body.setAttributeNS(null, "contenteditable", "true");
   var img = document.createElementNS("http://www.w3.org/1999/xhtml", "img");
diff --git a/editor/libeditor/tests/browserscope/lib/richtext2/richtext2/static/js/range.js b/editor/libeditor/tests/browserscope/lib/richtext2/richtext2/static/js/range.js
index 86ba6e1716f0..e6bfa84ba5a1 100644
--- a/editor/libeditor/tests/browserscope/lib/richtext2/richtext2/static/js/range.js
+++ b/editor/libeditor/tests/browserscope/lib/richtext2/richtext2/static/js/range.js
@@ -2109,7 +2109,7 @@ goog.dom.createTable_ = function(doc, rows, columns, fillWithNbsp) {
   totalHtml.push("</table>");
   var elem = doc.createElement(goog.dom.TagName.DIV);
   elem.innerHTML = totalHtml.join("");
-  return elem.removeChild(elem.firstChild)
+  return elem.firstChild.remove()
 };
 goog.dom.htmlToDocumentFragment = function(htmlString) {
   return goog.dom.htmlToDocumentFragment_(document, htmlString)
@@ -2118,12 +2118,12 @@ goog.dom.htmlToDocumentFragment_ = function(doc, htmlString) {
   var tempDiv = doc.createElement("div");
   if(goog.dom.BrowserFeature.INNER_HTML_NEEDS_SCOPED_ELEMENT) {
     tempDiv.innerHTML = "<br>" + htmlString;
-    tempDiv.removeChild(tempDiv.firstChild)
+    tempDiv.firstChild.remove()
   }else {
     tempDiv.innerHTML = htmlString
   }
   if(tempDiv.childNodes.length == 1) {
-    return tempDiv.removeChild(tempDiv.firstChild)
+    return tempDiv.firstChild.remove()
   }else {
     var fragment = doc.createDocumentFragment();
     while(tempDiv.firstChild) {
diff --git a/editor/libeditor/tests/file_select_all_without_body.html b/editor/libeditor/tests/file_select_all_without_body.html
index 70050a847409..3389538313d3 100644
--- a/editor/libeditor/tests/file_select_all_without_body.html
+++ b/editor/libeditor/tests/file_select_all_without_body.html
@@ -16,7 +16,7 @@ function boom()
 {
   var root = document.documentElement;
   while(root.firstChild) {
-    root.removeChild(root.firstChild);
+    root.firstChild.remove();
   }
   root.appendChild(document.createTextNode("Mozilla"));
   root.focus();
diff --git a/editor/libeditor/tests/test_bug612447.html b/editor/libeditor/tests/test_bug612447.html
index b06739288419..cdb9b22f1e1a 100644
--- a/editor/libeditor/tests/test_bug612447.html
+++ b/editor/libeditor/tests/test_bug612447.html
@@ -44,7 +44,7 @@ SimpleTest.waitForFocus(function() {
   var beforeB = snapshotWindow(win, true);
   is(b.textContent, "X", "Typing should work");
   while (b.firstChild) {
-    b.removeChild(b.firstChild);
+    b.firstChild.remove();
   }
   ok(editorCommandsEnabled(), "The editor commands should work");
 
@@ -58,7 +58,7 @@ SimpleTest.waitForFocus(function() {
   var afterB = snapshotWindow(win, true);
   is(b.textContent, "X", "Typing should work");
   while (b.firstChild) {
-    b.removeChild(b.firstChild);
+    b.firstChild.remove();
   }
   ok(editorCommandsEnabled(), "The editor commands should work");
 
diff --git a/gfx/tests/crashtests/595727-1.html b/gfx/tests/crashtests/595727-1.html
index 13b048f8226d..d2012c715395 100644
--- a/gfx/tests/crashtests/595727-1.html
+++ b/gfx/tests/crashtests/595727-1.html
@@ -6,7 +6,7 @@
 function doTest()
 {
   var r = document.documentElement;
-  while(r.firstChild) { r.removeChild(r.firstChild); }
+  while(r.firstChild) { r.firstChild.remove(); }
   var body = document.createElementNS("http://www.w3.org/1999/xhtml", "body"); 
   r.appendChild(body); 
   body.contentEditable = "true"; 
diff --git a/layout/base/crashtests/372550-1.html b/layout/base/crashtests/372550-1.html
index a1dd8ea5b8b9..778652f0b52b 100644
--- a/layout/base/crashtests/372550-1.html
+++ b/layout/base/crashtests/372550-1.html
@@ -11,7 +11,7 @@
   document.body.offsetWidth;
   var div = document.getElementById("x");
   div.id = "y";
-  div.removeChild(div.firstChild);
+  div.firstChild.remove();
 </script>
 </body>
 </html>
diff --git a/layout/base/crashtests/393661-1.html b/layout/base/crashtests/393661-1.html
index d2e256d5f3dc..b7ea19cd3c5a 100644
--- a/layout/base/crashtests/393661-1.html
+++ b/layout/base/crashtests/393661-1.html
@@ -7,7 +7,7 @@
 function boom()
 {
   var z = document.getElementById("z");
-  z.removeChild(z.firstChild);
+  z.firstChild.remove();
 }
 </script>
 </head>
diff --git a/layout/base/crashtests/403175-1.html b/layout/base/crashtests/403175-1.html
index 08764ff70769..a1c02a55396f 100644
--- a/layout/base/crashtests/403175-1.html
+++ b/layout/base/crashtests/403175-1.html
@@ -9,7 +9,7 @@ function boom()
   ++i;
   
   while (document.body.firstChild)
-    document.body.removeChild(document.body.firstChild);
+    document.body.firstChild.remove();
 
   var table = document.createElement("table");
   document.body.appendChild(table);
diff --git a/layout/base/crashtests/468578-1.xhtml b/layout/base/crashtests/468578-1.xhtml
index 278ff51ae538..3643e91d0ec0 100644
--- a/layout/base/crashtests/468578-1.xhtml
+++ b/layout/base/crashtests/468578-1.xhtml
@@ -8,7 +8,7 @@ function boom()
   var legend = document.getElementById("legend");
   legend.appendChild(document.createTextNode("T"));
   document.documentElement.offsetHeight;
-  legend.removeChild(legend.firstChild);
+  legend.firstChild.remove();
   document.body.removeChild(legend);
 }
 
diff --git a/layout/base/crashtests/538267-1.html b/layout/base/crashtests/538267-1.html
index c8942797482c..c192496cdfbb 100644
--- a/layout/base/crashtests/538267-1.html
+++ b/layout/base/crashtests/538267-1.html
@@ -8,7 +8,7 @@ div { -moz-column-count: 2; width: 0; }
 function boom()
 {
   var v = document.getElementById("v");
-  v.removeChild(v.firstChild);
+  v.firstChild.remove();
 }
 </script>
 </head>
diff --git a/layout/base/crashtests/852293.html b/layout/base/crashtests/852293.html
index d1098d080744..8c4783933d0a 100644
--- a/layout/base/crashtests/852293.html
+++ b/layout/base/crashtests/852293.html
@@ -57,7 +57,7 @@ function bounceDE()
 
 function clearChildren(root)
 {
-  while(root.firstChild) { root.removeChild(root.firstChild); }
+  while(root.firstChild) { root.firstChild.remove(); }
 }
 
 </script>
diff --git a/layout/base/crashtests/898913.html b/layout/base/crashtests/898913.html
index 39adbd463f8b..f81602a111e5 100644
--- a/layout/base/crashtests/898913.html
+++ b/layout/base/crashtests/898913.html
@@ -13,7 +13,7 @@ div:first-letter { float: right; }
 function boom()
 {
   var d = document.getElementById('d');
-  d.removeChild(d.firstChild);
+  d.firstChild.remove();
 }
 
 </script>
diff --git a/layout/generic/crashtests/413085-1.html b/layout/generic/crashtests/413085-1.html
index 8f1ddad97caf..edb752d5b503 100644
--- a/layout/generic/crashtests/413085-1.html
+++ b/layout/generic/crashtests/413085-1.html
@@ -10,7 +10,7 @@ body:first-letter { float: right; }
 
 function boom()
 {
-  document.body.removeChild(document.body.firstChild);
+  document.body.firstChild.remove();
   document.body.appendChild(document.createTextNode('x'));  
 }
 
diff --git a/layout/generic/crashtests/413085-2.html b/layout/generic/crashtests/413085-2.html
index bb82c6628078..6128304abdf6 100644
--- a/layout/generic/crashtests/413085-2.html
+++ b/layout/generic/crashtests/413085-2.html
@@ -5,7 +5,7 @@
 </style>
 <script>
   function boom() {
-   document.body.removeChild(document.body.firstChild);
+   document.body.firstChild.remove();
   }
 </script>
 </head>
diff --git a/layout/generic/crashtests/426040-1.html b/layout/generic/crashtests/426040-1.html
index 196a541cb04e..9863af7b834f 100644
--- a/layout/generic/crashtests/426040-1.html
+++ b/layout/generic/crashtests/426040-1.html
@@ -12,7 +12,7 @@ div { height: 1px; }
 function boom()
 {
   var a = document.getElementById("a"); 
-  a.removeChild(a.firstChild);
+  a.firstChild.remove();
   document.documentElement.style.outline = "none";
 }
 
diff --git a/layout/generic/crashtests/472776-1.html b/layout/generic/crashtests/472776-1.html
index 745dcc1676f8..be9a6a92d635 100644
--- a/layout/generic/crashtests/472776-1.html
+++ b/layout/generic/crashtests/472776-1.html
@@ -9,7 +9,7 @@ function boom()
   v.childNodes[1].firstChild.data = "";
   document.documentElement.offsetHeight;
   v.appendChild(document.createTextNode("D"));
-  v.removeChild(v.firstChild);
+  v.firstChild.remove();
 }
 
 </script>
diff --git a/layout/generic/crashtests/603490-1.html b/layout/generic/crashtests/603490-1.html
index f857c9f8379d..a9a8a8c2a3dd 100644
--- a/layout/generic/crashtests/603490-1.html
+++ b/layout/generic/crashtests/603490-1.html
@@ -3,7 +3,7 @@
 function boom()
 {
   while (document.documentElement.firstChild)
-    document.documentElement.removeChild(document.documentElement.firstChild);
+    document.documentElement.firstChild.remove();
   document.documentElement.contentEditable = "true";
   document.execCommand("strikethrough", false, null);
   try { document.execCommand("justifyfull", false, null); } catch(e) { }
diff --git a/layout/generic/crashtests/603510-1.html b/layout/generic/crashtests/603510-1.html
index 697845d07871..90d16bed2dbb 100644
--- a/layout/generic/crashtests/603510-1.html
+++ b/layout/generic/crashtests/603510-1.html
@@ -6,7 +6,7 @@ function boom()
   var r = document.documentElement;
 
   while (r.firstChild)
-    r.removeChild(r.firstChild);
+    r.firstChild.remove();
 
   var a = document.createTextNode("a");
   r.appendChild(a);
diff --git a/layout/generic/crashtests/667025.html b/layout/generic/crashtests/667025.html
index 29ef3d32b5e0..036aeda31921 100644
--- a/layout/generic/crashtests/667025.html
+++ b/layout/generic/crashtests/667025.html
@@ -11,7 +11,7 @@ function boom()
   document.documentElement.offsetHeight;
   var s = document.getElementById("s");
 
-  s.removeChild(s.firstChild);
+  s.firstChild.remove();
 
   document.documentElement.offsetHeight;
 }
diff --git a/layout/generic/crashtests/868906.html b/layout/generic/crashtests/868906.html
index f0b92c5a671a..24d3bfa3e88f 100644
--- a/layout/generic/crashtests/868906.html
+++ b/layout/generic/crashtests/868906.html
@@ -7,7 +7,7 @@
 function boom()
 {
   var root = document.documentElement;
-  while(root.firstChild) { root.removeChild(root.firstChild); }
+  while(root.firstChild) { root.firstChild.remove(); }
   root.appendChild(document.createElement("body"));
   root.offsetHeight;
 
diff --git a/layout/reftests/bidi/730562-1.html b/layout/reftests/bidi/730562-1.html
index 3b6ca3bf3c6e..b751b5120c77 100644
--- a/layout/reftests/bidi/730562-1.html
+++ b/layout/reftests/bidi/730562-1.html
@@ -11,7 +11,7 @@ function boom()
 
   // A dynamic change
   var x = document.getElementById("x");
-  x.removeChild(x.firstChild);
+  x.firstChild.remove();
   x.appendChild(document.createTextNode("\n\n\n"));
 }
 
diff --git a/layout/reftests/bugs/306660-3.html b/layout/reftests/bugs/306660-3.html
index c45be92a22e9..f8bd44235e4e 100644
--- a/layout/reftests/bugs/306660-3.html
+++ b/layout/reftests/bugs/306660-3.html
@@ -4,7 +4,7 @@
 <script>
   function loaded() {
     var f = document.getElementById("x");
-    f.removeChild(f.firstChild);
+    f.firstChild.remove();
   }
 </script>
 </head>
diff --git a/layout/reftests/bugs/398682-1.html b/layout/reftests/bugs/398682-1.html
index d9e0a1f8727e..0e5793b35232 100644
--- a/layout/reftests/bugs/398682-1.html
+++ b/layout/reftests/bugs/398682-1.html
@@ -37,7 +37,7 @@ function bounce()
     var docElemChildren = [];
     while (docElem.firstChild) {
         docElemChildren.push(docElem.firstChild);
-        docElem.removeChild(docElem.firstChild);
+        docElem.firstChild.remove();
     }
 
     for (var i = 0; i < docElemChildren.length; ++i)
diff --git a/layout/reftests/bugs/418766-1a.html b/layout/reftests/bugs/418766-1a.html
index 4187b8b10ac6..8dcfe6e19825 100644
--- a/layout/reftests/bugs/418766-1a.html
+++ b/layout/reftests/bugs/418766-1a.html
@@ -4,7 +4,7 @@
 function boom()
 {
   var n = document.getElementById("editMe");
-  n.removeChild(n.firstChild);
+  n.firstChild.remove();
   document.documentElement.className = "";
 }
 </script>
diff --git a/layout/reftests/bugs/421239-1.html b/layout/reftests/bugs/421239-1.html
index d4d94b0bacc6..d9cc8b5b4818 100644
--- a/layout/reftests/bugs/421239-1.html
+++ b/layout/reftests/bugs/421239-1.html
@@ -8,7 +8,7 @@
   function boom()
   {
     var a = document.getElementById("a");
-    a.removeChild(a.firstChild);
+    a.firstChild.remove();
     document.documentElement.className = "";
   }
   </script>
diff --git a/layout/reftests/bugs/421239-2.html b/layout/reftests/bugs/421239-2.html
index 39f5bf47e4c9..6db0b8e89cb5 100644
--- a/layout/reftests/bugs/421239-2.html
+++ b/layout/reftests/bugs/421239-2.html
@@ -8,7 +8,7 @@
   function boom()
   {
     var a = document.getElementById("a");
-    a.removeChild(a.firstChild);
+    a.firstChild.remove();
     document.documentElement.className = "";
   }
   </script>
diff --git a/layout/reftests/bugs/496840-1.html b/layout/reftests/bugs/496840-1.html
index 291d9abb2676..3901069e7de7 100644
--- a/layout/reftests/bugs/496840-1.html
+++ b/layout/reftests/bugs/496840-1.html
@@ -12,7 +12,7 @@ l.textContent = "#1";
 fs1.insertBefore(l, fs1.firstChild);
 
 var fs2 = document.getElementById("fs2");
-fs2.removeChild(fs2.firstChild);
+fs2.firstChild.remove();
 </script>
 </body>
 </html>
diff --git a/layout/reftests/forms/textarea/setvalue-framereconstruction-1.html b/layout/reftests/forms/textarea/setvalue-framereconstruction-1.html
index 2fe3b0d54a0f..03b3a4929032 100644
--- a/layout/reftests/forms/textarea/setvalue-framereconstruction-1.html
+++ b/layout/reftests/forms/textarea/setvalue-framereconstruction-1.html
@@ -22,7 +22,7 @@ function boom()
   document.getElementById("div").style.MozBinding = "url('#foo')";
 
   var opt1 = document.getElementById("opt1");
-  opt1.removeChild(opt1.firstChild);
+  opt1.firstChild.remove();
 
   document.getElementById("textarea").value += " y";
 
diff --git a/layout/reftests/table-anonymous-boxes/277995-1.html b/layout/reftests/table-anonymous-boxes/277995-1.html
index 61951ff0548f..e513d6a8fa49 100644
--- a/layout/reftests/table-anonymous-boxes/277995-1.html
+++ b/layout/reftests/table-anonymous-boxes/277995-1.html
@@ -4,7 +4,7 @@
   <script type="text/javascript" language="javascript">
     function doMore(data) {
       while(data.hasChildNodes()) 
-        data.removeChild(data.firstChild);
+        data.firstChild.remove();
       for (var i = 0; i < 10; i++) {
 	append(data);
       }
diff --git a/layout/reftests/table-anonymous-boxes/315146-1.xhtml b/layout/reftests/table-anonymous-boxes/315146-1.xhtml
index c282c8ef4474..13176bdc2b95 100644
--- a/layout/reftests/table-anonymous-boxes/315146-1.xhtml
+++ b/layout/reftests/table-anonymous-boxes/315146-1.xhtml
@@ -6,7 +6,7 @@
 	<script type="text/javascript"><![CDATA[
 	function DeleteRow(container) {
 		if (container.firstChild)
-			container.removeChild(container.firstChild);
+			container.firstChild.remove();
 	}
 
 	function AddRow(container) {
diff --git a/layout/reftests/xul-document-load/test005.js b/layout/reftests/xul-document-load/test005.js
index 21ae23e64bdf..726acd417b93 100644
--- a/layout/reftests/xul-document-load/test005.js
+++ b/layout/reftests/xul-document-load/test005.js
@@ -1,4 +1,4 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/licenses/publicdomain/  */
 
-document.removeChild(document.firstChild);
+document.firstChild.remove();
diff --git a/layout/style/crashtests/1277908-1.html b/layout/style/crashtests/1277908-1.html
index 6f9ca3bd0965..e02f45c4c889 100644
--- a/layout/style/crashtests/1277908-1.html
+++ b/layout/style/crashtests/1277908-1.html
@@ -1,6 +1,6 @@
 <script>
 window.onload = function () {
-  var root = document.documentElement; while(root.firstChild) { root.removeChild(root.firstChild); }
+  var root = document.documentElement; while(root.firstChild) { root.firstChild.remove(); }
   var a = document.createElementNS("http://www.w3.org/1999/xhtml", "link");
   a.setAttributeNS(null, "href", "mailto:");
   root.appendChild(a);
diff --git a/layout/style/test/test_bug98997.html b/layout/style/test/test_bug98997.html
index c7104c7c4713..103fa9237e54 100644
--- a/layout/style/test/test_bug98997.html
+++ b/layout/style/test/test_bug98997.html
@@ -74,7 +74,7 @@ function testReplaceChild(elt, text) {
 }
 
 function testRemoveChild(elt) {
-  elt.removeChild(elt.firstChild);
+  elt.firstChild.remove();
 }
 
 function testChangeData(elt, text) {
diff --git a/layout/style/test/test_flexbox_reflow_counts.html b/layout/style/test/test_flexbox_reflow_counts.html
index 01252883f01c..bfe041e5667a 100644
--- a/layout/style/test/test_flexbox_reflow_counts.html
+++ b/layout/style/test/test_flexbox_reflow_counts.html
@@ -60,7 +60,7 @@ function cleanup()
 {
   outerFlex.style = midFlex.style = innerBlock.style = "";
   while (innerBlock.firstChild) {
-    innerBlock.removeChild(innerBlock.firstChild);
+    innerBlock.firstChild.remove();
   }
 }
 
diff --git a/layout/tables/crashtests/460637-1.xhtml b/layout/tables/crashtests/460637-1.xhtml
index 50b3ef6a3c54..394c1a613cb8 100644
--- a/layout/tables/crashtests/460637-1.xhtml
+++ b/layout/tables/crashtests/460637-1.xhtml
@@ -4,7 +4,7 @@
 
   function boom() {
     var HTML_NS = "http://www.w3.org/1999/xhtml";
-    var r = document.documentElement; while(r.firstChild) { r.removeChild(r.firstChild); }
+    var r = document.documentElement; while(r.firstChild) { r.firstChild.remove(); }
     var table = document.createElementNS(HTML_NS, "table");
     table.setAttribute("border", "1");
     var text = document.createTextNode("\n ");
diff --git a/layout/tools/reftest/reftest.jsm b/layout/tools/reftest/reftest.jsm
index f4e9f2fa3479..587c8371e1e1 100644
--- a/layout/tools/reftest/reftest.jsm
+++ b/layout/tools/reftest/reftest.jsm
@@ -308,7 +308,7 @@ this.OnRefTestLoad = function OnRefTestLoad(win)
     if (Services.appinfo.OS == "Android") {
       let doc = gContainingWindow.document.getElementById('main-window');
       while (doc.hasChildNodes()) {
-        doc.removeChild(doc.firstChild);
+        doc.firstChild.remove();
       }
       doc.appendChild(gBrowser);
     } else {
diff --git a/security/manager/pki/resources/content/device_manager.js b/security/manager/pki/resources/content/device_manager.js
index 21db8ce097e7..efba5dba53a6 100644
--- a/security/manager/pki/resources/content/device_manager.js
+++ b/security/manager/pki/resources/content/device_manager.js
@@ -205,7 +205,7 @@ function enableButtons() {
 function ClearInfoList() {
   let infoList = document.getElementById("info_list");
   while (infoList.hasChildNodes()) {
-    infoList.removeChild(infoList.firstChild);
+    infoList.firstChild.remove();
   }
 }
 
@@ -221,7 +221,7 @@ function ClearDeviceList() {
   // module that just changed.
   let deviceList = document.getElementById("device_list");
   while (deviceList.hasChildNodes()) {
-    deviceList.removeChild(deviceList.firstChild);
+    deviceList.firstChild.remove();
   }
 }
 
diff --git a/security/manager/pki/resources/content/pippki.js b/security/manager/pki/resources/content/pippki.js
index 92b7bea322a4..8d85743fc575 100644
--- a/security/manager/pki/resources/content/pippki.js
+++ b/security/manager/pki/resources/content/pippki.js
@@ -16,7 +16,7 @@ function setText(id, value) {
     return;
   }
   if (element.hasChildNodes()) {
-    element.removeChild(element.firstChild);
+    element.firstChild.remove();
   }
   element.appendChild(document.createTextNode(value));
 }
diff --git a/toolkit/components/filepicker/content/filepicker.js b/toolkit/components/filepicker/content/filepicker.js
index 8dafcda9203f..c5e1ddd5339c 100644
--- a/toolkit/components/filepicker/content/filepicker.js
+++ b/toolkit/components/filepicker/content/filepicker.js
@@ -583,7 +583,7 @@ function populateAncestorList(directory) {
   var menu = document.getElementById("lookInMenu");
 
   while (menu.hasChildNodes()) {
-    menu.removeChild(menu.firstChild);
+    menu.firstChild.remove();
   }
 
   var menuItem = document.createElement("menuitem");
diff --git a/toolkit/components/printing/content/printjoboptions.js b/toolkit/components/printing/content/printjoboptions.js
index a7d928773314..280c594a4d98 100644
--- a/toolkit/components/printing/content/printjoboptions.js
+++ b/toolkit/components/printing/content/printjoboptions.js
@@ -81,7 +81,7 @@ paperListElement.prototype =
   {
     clearPaperList() {
           // remove the menupopup node child of the menulist.
-          this.paperListElement.removeChild(this.paperListElement.firstChild);
+          this.paperListElement.firstChild.remove();
         },
 
     appendPaperNames(aDataObject) {
diff --git a/toolkit/content/aboutProfiles.js b/toolkit/content/aboutProfiles.js
index 7ad3e1b952c8..798980af0a68 100644
--- a/toolkit/content/aboutProfiles.js
+++ b/toolkit/content/aboutProfiles.js
@@ -54,7 +54,7 @@ function findCurrentProfile() {
 function refreshUI() {
   let parent = document.getElementById("profiles");
   while (parent.firstChild) {
-    parent.removeChild(parent.firstChild);
+    parent.firstChild.remove();
   }
 
   let defaultProfile;
diff --git a/toolkit/content/tests/chrome/test_popup_recreate.xul b/toolkit/content/tests/chrome/test_popup_recreate.xul
index 14822acbd041..6c3fdcf57f1d 100644
--- a/toolkit/content/tests/chrome/test_popup_recreate.xul
+++ b/toolkit/content/tests/chrome/test_popup_recreate.xul
@@ -38,7 +38,7 @@ function recreate()
   if (gState == "before") {
     var element = document.getElementById("menulist");
     while (element.hasChildNodes())
-      element.removeChild(element.firstChild);
+      element.firstChild.remove();
     element.appendItem("Cat");
     gState = "after";
     document.getElementById("menulist").open = true;
diff --git a/toolkit/content/tests/chrome/test_tabbox.xul b/toolkit/content/tests/chrome/test_tabbox.xul
index 3cbacb15adfe..e664fb76de84 100644
--- a/toolkit/content/tests/chrome/test_tabbox.xul
+++ b/toolkit/content/tests/chrome/test_tabbox.xul
@@ -114,8 +114,8 @@ function test_tabbox()
   tabbox.selectedIndex = 0;
   test_tabpanels(tabpanels, tabbox);
 
-  tabs.removeChild(tabs.firstChild);
-  tabs.removeChild(tabs.firstChild);
+  tabs.firstChild.remove();
+  tabs.firstChild.remove();
 
   test_tabs(tabs);
 
diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index eb416af2865b..02fe11d383fa 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -1812,7 +1812,7 @@ extends="chrome://global/content/bindings/popup.xml#popup">
             return;
           }
           while (aDescriptionElement.hasChildNodes())
-            aDescriptionElement.removeChild(aDescriptionElement.firstChild);
+            aDescriptionElement.firstChild.remove();
 
           // If aNoEmphasis is specified, don't add any emphasis
           if (aNoEmphasis) {
diff --git a/toolkit/content/widgets/tree.xml b/toolkit/content/widgets/tree.xml
index 202e575009f8..299f26cdb490 100644
--- a/toolkit/content/widgets/tree.xml
+++ b/toolkit/content/widgets/tree.xml
@@ -1487,7 +1487,7 @@
           <![CDATA[
             // We no longer cache the picker content, remove the old content.
             while (aPopup.childNodes.length > 2)
-              aPopup.removeChild(aPopup.firstChild);
+              aPopup.firstChild.remove();
 
             var refChild = aPopup.firstChild;
 
diff --git a/toolkit/mozapps/extensions/content/extensions.js b/toolkit/mozapps/extensions/content/extensions.js
index 64d9c69727b8..4f1c67ef32e2 100644
--- a/toolkit/mozapps/extensions/content/extensions.js
+++ b/toolkit/mozapps/extensions/content/extensions.js
@@ -2505,7 +2505,7 @@ var gSearchView = {
       AddonRepository.cancelSearch();
 
     while (this._listBox.firstChild.localName == "richlistitem")
-      this._listBox.removeChild(this._listBox.firstChild);
+      this._listBox.firstChild.remove();
 
     gCachedAddons = {};
     this._pendingSearches = 2;
@@ -3820,7 +3820,7 @@ var gUpdatesView = {
         this._updateSelected.hidden = true;
 
         while (this._listBox.childNodes.length > 0)
-          this._listBox.removeChild(this._listBox.firstChild);
+          this._listBox.firstChild.remove();
       }
 
       var elements = [];
diff --git a/toolkit/mozapps/extensions/content/xpinstallConfirm.js b/toolkit/mozapps/extensions/content/xpinstallConfirm.js
index 085f6186ea23..21d8dd777f04 100644
--- a/toolkit/mozapps/extensions/content/xpinstallConfirm.js
+++ b/toolkit/mozapps/extensions/content/xpinstallConfirm.js
@@ -77,7 +77,7 @@ XPInstallConfirm.init = function() {
   var textNode = document.createTextNode(introString);
   var introNode = document.getElementById("itemWarningIntro");
   while (introNode.hasChildNodes())
-    introNode.removeChild(introNode.firstChild);
+    introNode.firstChild.remove();
   introNode.appendChild(textNode);
 
   var okButton = document.documentElement.getButton("accept");
diff --git a/toolkit/mozapps/preferences/fontbuilder.js b/toolkit/mozapps/preferences/fontbuilder.js
index dc8a4ca3b8e2..e0557e346c0a 100644
--- a/toolkit/mozapps/preferences/fontbuilder.js
+++ b/toolkit/mozapps/preferences/fontbuilder.js
@@ -19,7 +19,7 @@ var FontBuilder = {
   buildFontList(aLanguage, aFontType, aMenuList) {
     // Reset the list
     while (aMenuList.hasChildNodes())
-      aMenuList.removeChild(aMenuList.firstChild);
+      aMenuList.firstChild.remove();
 
     var defaultFont = null;
     // Load Font Lists
diff --git a/toolkit/mozapps/update/content/history.js b/toolkit/mozapps/update/content/history.js
index 4c5e70a2e3fe..60d12da31c61 100644
--- a/toolkit/mozapps/update/content/history.js
+++ b/toolkit/mozapps/update/content/history.js
@@ -20,7 +20,7 @@ var gUpdateHistory = {
     var uc = um.updateCount;
     if (uc) {
       while (this._view.hasChildNodes())
-        this._view.removeChild(this._view.firstChild);
+        this._view.firstChild.remove();
 
       var bundle = document.getElementById("updateBundle");
 
diff --git a/toolkit/mozapps/update/content/updates.js b/toolkit/mozapps/update/content/updates.js
index 0e961230f146..b21d5605b50e 100644
--- a/toolkit/mozapps/update/content/updates.js
+++ b/toolkit/mozapps/update/content/updates.js
@@ -805,7 +805,7 @@ var gDownloadingPage = {
     if (this._downloadStatus.textContent == status)
       return;
     while (this._downloadStatus.hasChildNodes())
-      this._downloadStatus.removeChild(this._downloadStatus.firstChild);
+      this._downloadStatus.firstChild.remove();
     this._downloadStatus.appendChild(document.createTextNode(status));
   },
 
diff --git a/toolkit/mozapps/update/content/updates.xml b/toolkit/mozapps/update/content/updates.xml
index 9e8d4e9368fb..9218f433fd11 100644
--- a/toolkit/mozapps/update/content/updates.xml
+++ b/toolkit/mozapps/update/content/updates.xml
@@ -73,7 +73,7 @@
           this.setAttribute("status", val);
           var field = document.getAnonymousElementByAttribute(this, "class", "update-status-value");
           while (field.hasChildNodes())
-            field.removeChild(field.firstChild);
+            field.firstChild.remove();
           field.appendChild(document.createTextNode(val));
           return val;
         ]]></setter>
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/avoid-removeChild.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/avoid-removeChild.js
index eafa600bdb76..4b92a02af2d9 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/avoid-removeChild.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/avoid-removeChild.js
@@ -27,17 +27,27 @@ module.exports = function(context) {
       if (callee.type !== "MemberExpression" ||
           callee.property.type !== "Identifier" ||
           callee.property.name != "removeChild" ||
-          callee.object.type != "MemberExpression" ||
-          callee.object.property.type != "Identifier" ||
-          callee.object.property.name != "parentNode" ||
-          helpers.getASTSource(callee.object.object) !=
-            helpers.getASTSource(node.arguments[0]) ||
           node.arguments.length != 1) {
         return;
       }
 
-      context.report(node, "use element.remove() instead of " +
-                           "element.parentNode.removeChild(element)");
+      if (callee.object.type == "MemberExpression" &&
+          callee.object.property.type == "Identifier" &&
+          callee.object.property.name == "parentNode" &&
+          helpers.getASTSource(callee.object.object) ==
+            helpers.getASTSource(node.arguments[0])) {
+        context.report(node, "use element.remove() instead of " +
+                             "element.parentNode.removeChild(element)");
+      }
+
+      if (node.arguments[0].type == "MemberExpression" &&
+          node.arguments[0].property.type == "Identifier" &&
+          node.arguments[0].property.name == "firstChild" &&
+          helpers.getASTSource(callee.object) ==
+            helpers.getASTSource(node.arguments[0].object)) {
+        context.report(node, "use element.firstChild.remove() instead of " +
+                             "element.removeChild(element.firstChild)");
+      }
     }
   };
 };
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/package.json b/tools/lint/eslint/eslint-plugin-mozilla/package.json
index d4174152bd00..9d1477125c38 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/package.json
+++ b/tools/lint/eslint/eslint-plugin-mozilla/package.json
@@ -1,6 +1,6 @@
 {
   "name": "eslint-plugin-mozilla",
-  "version": "0.2.26",
+  "version": "0.2.27",
   "description": "A collection of rules that help enforce JavaScript coding standard in the Mozilla project.",
   "keywords": [
     "eslint",
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/tests/avoid-removeChild.js b/tools/lint/eslint/eslint-plugin-mozilla/tests/avoid-removeChild.js
index 3ecd1378ea04..61b371b4e247 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/tests/avoid-removeChild.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/tests/avoid-removeChild.js
@@ -13,9 +13,11 @@ var rule = require("../lib/rules/avoid-removeChild");
 // Tests
 //------------------------------------------------------------------------------
 
-function invalidCode(code) {
-  let message = "use element.remove() instead of " +
-                "element.parentNode.removeChild(element)";
+function invalidCode(code, message) {
+  if (!message) {
+    message = "use element.remove() instead of " +
+              "element.parentNode.removeChild(element)";
+  }
   return {code: code, errors: [{message: message, type: "CallExpression"}]};
 }
 
@@ -31,7 +33,10 @@ exports.runTest = function(ruleTester) {
       invalidCode("elt.parentNode.removeChild(elt);"),
       invalidCode("elt.parentNode.parentNode.removeChild(elt.parentNode);"),
       invalidCode("$(e).parentNode.removeChild($(e));"),
-      invalidCode("$('e').parentNode.removeChild($('e'));")
+      invalidCode("$('e').parentNode.removeChild($('e'));"),
+      invalidCode("elt.removeChild(elt.firstChild);",
+                  "use element.firstChild.remove() instead of " +
+                  "element.removeChild(element.firstChild)")
     ]
   });
 };