diff --git a/editor/libeditor/HTMLEditSubActionHandler.cpp b/editor/libeditor/HTMLEditSubActionHandler.cpp
index b28dfb632af2..b62dde653854 100644
--- a/editor/libeditor/HTMLEditSubActionHandler.cpp
+++ b/editor/libeditor/HTMLEditSubActionHandler.cpp
@@ -12042,7 +12042,9 @@ HTMLEditor::InsertPaddingBRElementIfNeeded(
           HTMLEditUtils::IsInlineContent(
               *nextVisibleThing.ElementPtr(),
               BlockInlineCheck::UseHTMLDefaultStyle)) {
-        return EditorDOMPoint::AtEndOf(*nextVisibleThing.ElementPtr());
+        return nextVisibleThing.ReachedCurrentBlockBoundary()
+                   ? EditorDOMPoint::AtEndOf(*nextVisibleThing.ElementPtr())
+                   : EditorDOMPoint(nextVisibleThing.ElementPtr());
       }
     }
     return HTMLEditUtils::LineRequiresPaddingLineBreakToBeVisible(aPoint,
diff --git a/editor/libeditor/tests/mochitest.toml b/editor/libeditor/tests/mochitest.toml
index 42967ab3546c..25597ff5c258 100644
--- a/editor/libeditor/tests/mochitest.toml
+++ b/editor/libeditor/tests/mochitest.toml
@@ -476,6 +476,9 @@ skip-if = ["display == 'wayland'"] # Bug 1935188
 
 ["test_label_contenteditable.html"]
 
+["test_mailcite_backspace_at_end_of_inline_reply.html"]
+skip-if = ["xorigin"] # Testing internal API for comm-central
+
 ["test_mailcite_keep_trailing_br_after_delete.html"]
 skip-if = ["xorigin"] # Testing internal API for comm-central
 
diff --git a/editor/libeditor/tests/test_mailcite_backspace_at_end_of_inline_reply.html b/editor/libeditor/tests/test_mailcite_backspace_at_end_of_inline_reply.html
new file mode 100644
index 000000000000..2ee315a69595
--- /dev/null
+++ b/editor/libeditor/tests/test_mailcite_backspace_at_end_of_inline_reply.html
@@ -0,0 +1,88 @@
+<!doctype html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Trailing &lt;br&gt; of a mailcite which is a blocked &lt;span&gt;</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+<script>
+"use strict";
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(async () => {
+  const iframe = document.querySelector("iframe");
+  await new Promise(resolve => {
+    if (iframe.contentDocument?.readyState == "complete") {
+      resolve();
+      return;
+    }
+    iframe.addEventListener("load", resolve, {once: true});
+  });
+
+
+  const win = iframe.contentWindow;
+  getEditor(win).flags |=
+    SpecialPowers.Ci.nsIEditor.eEditorMailMask | SpecialPowers.Ci.nsIEditor.eEditorPlaintextMask;
+  const doc = iframe.contentDocument;
+  const mailEditor = getEditorMailSupport(win);
+  win.focus();
+  doc.body.focus();
+  const mailciteStyle = "white-space: pre-wrap; display: block; width: 98vw;";
+  const mailcite = SpecialPowers.unwrap(
+    mailEditor.insertAsCitedQuotation("Hi there, How are you doing.", "", false)
+  );
+  is(
+    doc.body.innerHTML,
+    `<span style="${mailciteStyle}">&gt; Hi there, How are you doing.<br><br></span><br><br>`,
+    "nsIEditorMailSupport.insertAsCitedQuotation() should insert a mailcite span"
+  );
+  // Put caret before "How".
+  win.getSelection().collapse(mailcite.firstChild, "> Hi there, ".length);
+  doc.execCommand("insertParagraph"); // Type Enter
+  doc.execCommand("insertText", false, "Here is inline reply.");
+  doc.execCommand("delete"); // Type Backspace
+  doc.execCommand("delete"); // Type Backspace
+  doc.execCommand("delete"); // Type Backspace
+  is(
+    doc.body.innerHTML,
+    `<span style="${mailciteStyle}">&gt; Hi there, <br></span>` + // FIXME: The last white-space should be an NBSP...
+    `Here is inline rep<br>` + // The last <br> is required for giving different lines after serializing this as plaintext.
+    `<span style="${mailciteStyle}">How are you doing.<br><br></span><br><br>`,
+    "Backspace shouldn't cause inserting linebreaks at end of the second quote #1"
+  );
+  doc.execCommand("delete"); // Type Backspace
+  doc.execCommand("delete"); // Type Backspace
+  doc.execCommand("delete"); // Type Backspace
+  is(
+    doc.body.innerHTML,
+    `<span style="${mailciteStyle}">&gt; Hi there, <br></span>` + // FIXME: The last white-space should be an NBSP...
+    `Here is inline&nbsp;<br>` + // The last <br> is required for giving different lines after serializing this as plaintext.
+    `<span style="${mailciteStyle}">How are you doing.<br><br></span><br><br>`,
+    "Backspace shouldn't cause inserting linebreaks at end of the second quote #2"
+  );
+  doc.execCommand("delete"); // Type Backspace
+  is(
+    doc.body.innerHTML,
+    `<span style="${mailciteStyle}">&gt; Hi there, <br></span>` + // FIXME: The last white-space should be an NBSP...
+    `Here is inline<br>` + // The last <br> is required for giving different lines after serializing this as plaintext.
+    `<span style="${mailciteStyle}">How are you doing.<br><br></span><br><br>`,
+    "Backspace shouldn't cause inserting linebreaks at end of the second quote #3"
+  );
+
+  SimpleTest.finish();
+});
+
+function getEditor(aWindow) {
+  const editingSession = SpecialPowers.wrap(aWindow).docShell.editingSession;
+  return editingSession.getEditorForWindow(aWindow);
+}
+
+function getEditorMailSupport(aWindow) {
+  return getEditor(aWindow).QueryInterface(SpecialPowers.Ci.nsIEditorMailSupport);
+}
+</script>
+</head>
+<body>
+  <iframe srcdoc="<body contenteditable><br><br></body>"></iframe>
+</body>
+</html>
