Bug 1577257 - Share logic behind panel headers across the UI r=willdurand,Gijs,fluent-reviewers,flod

Differential Revision: https://phabricator.services.mozilla.com/D160972

browser/components/customizableui/PanelMultiView.jsm

@@ -1374,20 +1374,27 @@ var PanelView = class extends AssociatedToNode {
     };
 
     // If the header already exists, update or remove it as requested.
-    let header = this.node.firstElementChild;
-    if (header && header.classList.contains("panel-header")) {
-      if (value) {
-        // The back button has a label in it - we want to select
-        // the label that's a direct child of the header.
-        header.querySelector(".panel-header > h1 > span").textContent = value;
-        ensureHeaderSeparator(header);
-      } else {
+    let header = this.node.querySelector(".panel-header");
+    if (header) {
+      if (!this.node.getAttribute("mainview")) {
+        if (value) {
+          // The back button has a label in it - we want to select
+          // the span that's a child of the header.
+          header.querySelector(".panel-header > h1 > span").textContent = value;
+          ensureHeaderSeparator(header);
+        } else {
+          if (header.nextSibling.tagName == "toolbarseparator") {
+            header.nextSibling.remove();
+          }
+          header.remove();
+        }
+        return;
+      } else if (!this.node.getAttribute("showheader")) {
         if (header.nextSibling.tagName == "toolbarseparator") {
           header.nextSibling.remove();
         }
         header.remove();
       }
-      return;
     }
 
     // The header doesn't exist, only create it if needed.

browser/components/customizableui/content/panelUI.inc.xhtml

@@ -74,9 +74,12 @@
          hidden="true">
     <panelmultiview mainViewId="unified-extensions-view">
       <panelview id="unified-extensions-view"
-                 class="cui-widget-panelview">
-        <vbox class="unified-extensions-panel-header">
-          <html:h1 data-l10n-id="unified-extensions-header-title"/>
+                 class="cui-widget-panelview"
+                 showheader="true">
+        <vbox class="panel-header">
+          <html:h1>
+            <html:span data-l10n-id="unified-extensions-header-title"/>
+          </html:h1>
         </vbox>
 
         <toolbarseparator />