Backed out changeset e3b15fe52734 (bug 1265800) for failing added wpt /XMLHttpRequest/event-error.html. r=backout

editor/libeditor/HTMLEditRules.cpp

@@ -2294,11 +2294,24 @@ HTMLEditRules::WillDeleteSelection(Selection* aSelection,
         NS_ENSURE_STATE(mHTMLEditor);
         if (leftBlockParent == rightBlockParent &&
             mHTMLEditor->NodesSameType(GetAsDOMNode(leftParent),
-                                       GetAsDOMNode(rightParent)) &&
-            // XXX What's special about these three types of block?
-            (leftParent->IsHTMLElement(nsGkAtoms::p) ||
-             HTMLEditUtils::IsListItem(leftParent) ||
-             HTMLEditUtils::IsHeader(*leftParent))) {
+                                       GetAsDOMNode(rightParent))) {
+          if (leftParent->IsHTMLElement(nsGkAtoms::p)) {
+            // First delete the selection
+            NS_ENSURE_STATE(mHTMLEditor);
+            res = mHTMLEditor->DeleteSelectionImpl(aAction, aStripWrappers);
+            NS_ENSURE_SUCCESS(res, res);
+            // Then join paragraphs, insert break
+            NS_ENSURE_STATE(mHTMLEditor);
+            EditorDOMPoint pt =
+              mHTMLEditor->JoinNodeDeep(*leftParent, *rightParent);
+            NS_ENSURE_STATE(pt.node);
+            // Fix up selection
+            res = aSelection->Collapse(pt.node, pt.offset);
+            NS_ENSURE_SUCCESS(res, res);
+            return NS_OK;
+          }
+          if (HTMLEditUtils::IsListItem(leftParent) ||
+              HTMLEditUtils::IsHeader(*leftParent)) {
             // First delete the selection
             NS_ENSURE_STATE(mHTMLEditor);
             res = mHTMLEditor->DeleteSelectionImpl(aAction, aStripWrappers);
@@ -2312,6 +2325,7 @@ HTMLEditRules::WillDeleteSelection(Selection* aSelection,
             res = aSelection->Collapse(pt.node, pt.offset);
             NS_ENSURE_SUCCESS(res, res);
             return NS_OK;
+          }
         }
 
         // Else blocks not same type, or not siblings.  Delete everything