--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -983,18 +983,25 @@ nsFrameLoader::AddTreeItemToTreeOwner(ns
                                       nsIDocShellTreeOwner* aOwner,
                                       int32_t aParentType,
                                       nsIDocShell* aParentNode)
 {
   NS_PRECONDITION(aItem, "Must have docshell treeitem");
   NS_PRECONDITION(mOwnerContent, "Must have owning content");
 
   nsAutoString value;
-  bool isContent = mOwnerContent->AttrValueIs(
-    kNameSpaceID_None, TypeAttrName(), nsGkAtoms::content, eIgnoreCase);
+  bool isContent = false;
+  mOwnerContent->GetAttr(kNameSpaceID_None, TypeAttrName(), value);
+
+  // we accept "content" and "content-xxx" values.
+  // We ignore anything that comes after 'content-'.
+  isContent = value.LowerCaseEqualsLiteral("content") ||
+    StringBeginsWith(value, NS_LITERAL_STRING("content-"),
+                     nsCaseInsensitiveStringComparator());
+
 
   // Force mozbrowser frames to always be typeContent, even if the
   // mozbrowser interfaces are disabled.
   nsCOMPtr<nsIDOMMozBrowserFrame> mozbrowser =
     do_QueryInterface(mOwnerContent);
   if (mozbrowser) {
     bool isMozbrowser = false;
     mozbrowser->GetMozbrowser(&isMozbrowser);
@@ -2888,18 +2895,22 @@ nsFrameLoader::TryRemoteBrowser()
         return false;
       }
     }
 
     if (!mOwnerContent->IsXULElement()) {
       return false;
     }
 
-    if (!mOwnerContent->AttrValueIs(kNameSpaceID_None, nsGkAtoms::type,
-                                    nsGkAtoms::content, eIgnoreCase)) {
+    nsAutoString value;
+    mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::type, value);
+
+    if (!value.LowerCaseEqualsLiteral("content") &&
+        !StringBeginsWith(value, NS_LITERAL_STRING("content-"),
+                          nsCaseInsensitiveStringComparator())) {
       return false;
     }
 
     // Try to get the related content parent from our browser element.
     openerContentParent = GetContentParent(mOwnerContent);
   }
 
   uint32_t chromeFlags = 0;
@@ -3349,17 +3360,23 @@ nsFrameLoader::AttributeChanged(nsIDocum
   if (!is_primary) {
     nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
     if (pm)
       pm->HidePopupsInDocShell(mDocShell);
   }
 #endif
 
   parentTreeOwner->ContentShellRemoved(mDocShell);
-  if (aElement->AttrValueIs(kNameSpaceID_None, TypeAttrName(), nsGkAtoms::content, eIgnoreCase)) {
+
+  nsAutoString value;
+  aElement->GetAttr(kNameSpaceID_None, TypeAttrName(), value);
+
+  if (value.LowerCaseEqualsLiteral("content") ||
+      StringBeginsWith(value, NS_LITERAL_STRING("content-"),
+                       nsCaseInsensitiveStringComparator())) {
     parentTreeOwner->ContentShellAdded(mDocShell, is_primary);
   }
 }
 
 /**
  * Send the RequestNotifyAfterRemotePaint message to the current Tab.
  */
 NS_IMETHODIMP