diff --git a/editor/libeditor/WSRunObject.cpp b/editor/libeditor/WSRunObject.cpp
index 8b0ba37c4fe2..0fb5bd3ae1c0 100644
--- a/editor/libeditor/WSRunObject.cpp
+++ b/editor/libeditor/WSRunObject.cpp
@@ -654,22 +654,26 @@ nsresult WSRunObject::AdjustWhitespace() {
 
 
 
-nsINode* WSRunScanner::GetWSBoundingParent() const {
-  if (NS_WARN_IF(!mScanStartPoint.IsSet())) {
+nsIContent* WSRunScanner::GetEditableBlockParentOrTopmotEditableInlineContent(
+    nsIContent* aContent) const {
+  if (NS_WARN_IF(!aContent)) {
     return nullptr;
   }
+  NS_ASSERTION(mHTMLEditor->IsEditable(aContent),
+               "Given content is not editable");
   
   
   
-  OwningNonNull<nsINode> wsBoundingParent = *mScanStartPoint.GetContainer();
-  while (!IsBlockNode(wsBoundingParent)) {
-    nsCOMPtr<nsINode> parent = wsBoundingParent->GetParentNode();
-    if (!parent || !mHTMLEditor->IsEditable(parent)) {
+  nsIContent* editableBlockParentOrTopmotEditableInlineContent = nullptr;
+  for (nsIContent* content = aContent;
+       content && mHTMLEditor->IsEditable(content);
+       content = content->GetParent()) {
+    editableBlockParentOrTopmotEditableInlineContent = content;
+    if (IsBlockNode(editableBlockParentOrTopmotEditableInlineContent)) {
       break;
     }
-    wsBoundingParent = parent;
   }
-  return wsBoundingParent;
+  return editableBlockParentOrTopmotEditableInlineContent;
 }
 
 nsresult WSRunScanner::GetWSNodes() {
@@ -677,7 +681,20 @@ nsresult WSRunScanner::GetWSNodes() {
   
   
   EditorDOMPoint start(mScanStartPoint), end(mScanStartPoint);
-  nsCOMPtr<nsINode> wsBoundingParent = GetWSBoundingParent();
+  nsIContent* scanStartContent = mScanStartPoint.GetContainerAsContent();
+  if (NS_WARN_IF(!scanStartContent)) {
+    
+    
+    
+    
+    return NS_ERROR_FAILURE;
+  }
+  nsIContent* editableBlockParentOrTopmotEditableInlineContent =
+      GetEditableBlockParentOrTopmotEditableInlineContent(scanStartContent);
+  if (NS_WARN_IF(!editableBlockParentOrTopmotEditableInlineContent)) {
+    
+    editableBlockParentOrTopmotEditableInlineContent = scanStartContent;
+  }
 
   
   if (Text* textNode = mScanStartPoint.GetContainerAsText()) {
@@ -715,7 +732,8 @@ nsresult WSRunScanner::GetWSNodes() {
 
   while (!mStartNode) {
     
-    nsCOMPtr<nsIContent> priorNode = GetPreviousWSNode(start, wsBoundingParent);
+    nsCOMPtr<nsIContent> priorNode = GetPreviousWSNode(
+        start, editableBlockParentOrTopmotEditableInlineContent);
     if (priorNode) {
       if (IsBlockNode(priorNode)) {
         mStartNode = start.GetContainer();
@@ -777,10 +795,13 @@ nsresult WSRunScanner::GetWSNodes() {
       }
     } else {
       
+      
       mStartNode = start.GetContainer();
       mStartOffset = start.Offset();
       mStartReason = WSType::thisBlock;
-      mStartReasonNode = wsBoundingParent;
+      
+      
+      mStartReasonNode = editableBlockParentOrTopmotEditableInlineContent;
     }
   }
 
@@ -820,7 +841,8 @@ nsresult WSRunScanner::GetWSNodes() {
 
   while (!mEndNode) {
     
-    nsCOMPtr<nsIContent> nextNode = GetNextWSNode(end, wsBoundingParent);
+    nsCOMPtr<nsIContent> nextNode =
+        GetNextWSNode(end, editableBlockParentOrTopmotEditableInlineContent);
     if (nextNode) {
       if (IsBlockNode(nextNode)) {
         
@@ -884,10 +906,13 @@ nsresult WSRunScanner::GetWSNodes() {
       }
     } else {
       
+      
       mEndNode = end.GetContainer();
       mEndOffset = end.Offset();
       mEndReason = WSType::thisBlock;
-      mEndReasonNode = wsBoundingParent;
+      
+      
+      mEndReasonNode = editableBlockParentOrTopmotEditableInlineContent;
     }
   }
 
@@ -1839,7 +1864,9 @@ nsresult WSRunObject::CheckTrailingNBSPOfRun(WSFragment* aRun) {
         rightCheck = true;
       }
       if ((aRun->mRightType & WSType::block) &&
-          IsBlockNode(GetWSBoundingParent())) {
+          (IsBlockNode(GetEditableBlockParentOrTopmotEditableInlineContent(
+               mScanStartPoint.GetContainerAsContent())) ||
+           IsBlockNode(mScanStartPoint.GetContainerAsContent()))) {
         RefPtr<Selection> selection = htmlEditor->GetSelection();
         if (NS_WARN_IF(!selection)) {
           return NS_ERROR_FAILURE;
diff --git a/editor/libeditor/WSRunObject.h b/editor/libeditor/WSRunObject.h
index d41353220869..8a7e21e3c182 100644
--- a/editor/libeditor/WSRunObject.h
+++ b/editor/libeditor/WSRunObject.h
@@ -295,8 +295,8 @@ class MOZ_STACK_CLASS WSRunScanner {
 
 
 
-
-  nsINode* GetWSBoundingParent() const;
+  nsIContent* GetEditableBlockParentOrTopmotEditableInlineContent(
+      nsIContent* aContent) const;
 
   static bool IsBlockNode(nsINode* aNode);
 
diff --git a/editor/libeditor/crashtests/crashtests.list b/editor/libeditor/crashtests/crashtests.list
index ca010200f897..5fdd77d50176 100644
--- a/editor/libeditor/crashtests/crashtests.list
+++ b/editor/libeditor/crashtests/crashtests.list
@@ -80,7 +80,7 @@ load 1348851.html
 load 1350772.html
 load 1364133.html
 load 1366176.html
-load 1375131.html
+asserts(3) load 1375131.html # assertion in WSRunScanner::GetEditableBlockParentOrTopmotEditableInlineContent()
 load 1381541.html
 load 1383747.html
 load 1383755.html
@@ -94,7 +94,7 @@ load 1402526.html
 pref(dom.document.exec_command.nested_calls_allowed,true) asserts(1) load 1402904.html # assertion is that mutation event listener caused by execCommand calls another execCommand
 pref(dom.document.exec_command.nested_calls_allowed,true) asserts(1) load 1405747.html # assertion is that mutation event listener caused by execCommand calls another execCommand
 load 1405897.html
-load 1408170.html
+asserts(3) load 1408170.html # assertion in WSRunScanner::GetEditableBlockParentOrTopmotEditableInlineContent()
 asserts(0-1) load 1414581.html
 load 1415231.html
 load 1423767.html
@@ -111,7 +111,7 @@ pref(layout.accessiblecaret.enabled,true) load 1470926.html
 pref(dom.document.exec_command.nested_calls_allowed,true) asserts(1) load 1474978.html # assertion is that mutation event listener caused by execCommand calls another execCommand
 load 1525481.html
 load 1533913.html
-load 1534394.html
+asserts(4) load 1534394.html # assertion in WSRunScanner::GetEditableBlockParentOrTopmotEditableInlineContent()
 load 1547897.html
 load 1547898.html
 load 1556799.html
diff --git a/editor/libeditor/tests/test_bug430392.html b/editor/libeditor/tests/test_bug430392.html
index ddac5f6fe62f..59ea105f4d67 100644
--- a/editor/libeditor/tests/test_bug430392.html
+++ b/editor/libeditor/tests/test_bug430392.html
@@ -110,6 +110,11 @@
   SimpleTest.finish();
 }
 
+// In WSRunScanner::GetEditableBlockParentOrTopmotEditableInlineContent().
+// Before it, HTMLEditor must be able to stop handling edit action at
+// non-editable content.
+SimpleTest.expectAssertions(18);
+
 SimpleTest.waitForExplicitFinish();
 SimpleTest.waitForFocus(test);
 
diff --git a/testing/web-platform/meta/editing/run/inserthtml.html.ini b/testing/web-platform/meta/editing/run/inserthtml.html.ini
index 06bfca8cd941..e8fdf4bbe1d6 100644
--- a/testing/web-platform/meta/editing/run/inserthtml.html.ini
+++ b/testing/web-platform/meta/editing/run/inserthtml.html.ini
@@ -1,4 +1,6 @@
 [inserthtml.html]
+  min-asserts: 14
+  max-asserts: 14
   prefs: [editor.use_div_for_default_newlines:true]
   [[["stylewithcss","true"\],["inserthtml","ab<b>c</b>d"\]\] "[foo<span style=color:#aBcDeF>bar\]</span>baz" compare innerHTML]
     expected: FAIL