diff --git a/mozilla/content/base/src/nsScriptLoader.cpp b/mozilla/content/base/src/nsScriptLoader.cpp
index e7ec96c9d9d..1bb68913f1c 100644
--- a/mozilla/content/base/src/nsScriptLoader.cpp
+++ b/mozilla/content/base/src/nsScriptLoader.cpp
@@ -171,6 +171,12 @@ nsScriptLoader::~nsScriptLoader()
   for (PRInt32 i = 0; i < mPendingRequests.Count(); i++) {
     mPendingRequests[i]->FireScriptAvailable(NS_ERROR_ABORT);
   }
+
+  // Unblock the kids, in case any of them moved to a different document
+  // subtree in the meantime and therefore aren't actually going away.
+  for (PRUint32 j = 0; j < mPendingChildLoaders.Length(); ++j) {
+    mPendingChildLoaders[j]->RemoveExecuteBlocker();
+  }  
 }
 
 NS_IMPL_ISUPPORTS1(nsScriptLoader, nsIStreamLoaderObserver)
@@ -636,7 +642,7 @@ nsScriptLoader::EvaluateScript(nsScriptLoadRequest* aRequest,
 void
 nsScriptLoader::ProcessPendingRequestsAsync()
 {
-  if (mPendingRequests.Count()) {
+  if (mPendingRequests.Count() || !mPendingChildLoaders.IsEmpty()) {
     nsCOMPtr<nsIRunnable> ev = new nsRunnableMethod<nsScriptLoader>(this,
       &nsScriptLoader::ProcessPendingRequests);
 
@@ -653,6 +659,33 @@ nsScriptLoader::ProcessPendingRequests()
     mPendingRequests.RemoveObjectAt(0);
     ProcessRequest(request);
   }
+
+  while (ReadyToExecuteScripts() && !mPendingChildLoaders.IsEmpty()) {
+    nsRefPtr<nsScriptLoader> child = mPendingChildLoaders[0];
+    mPendingChildLoaders.RemoveElementAt(0);
+    child->RemoveExecuteBlocker();
+  }
+}
+
+PRBool
+nsScriptLoader::ReadyToExecuteScripts()
+{
+  // Make sure the SelfReadyToExecuteScripts check is first, so that
+  // we don't block twice on an ancestor.
+  if (!SelfReadyToExecuteScripts()) {
+    return PR_FALSE;
+  }
+  
+  for (nsIDocument* doc = mDocument; doc; doc = doc->GetParentDocument()) {
+    nsScriptLoader* ancestor = doc->ScriptLoader();
+    if (!ancestor->SelfReadyToExecuteScripts() &&
+        ancestor->AddPendingChildLoader(this)) {
+      AddExecuteBlocker();
+      return PR_FALSE;
+    }
+  }
+
+  return PR_TRUE;
 }
 
 
diff --git a/mozilla/content/base/src/nsScriptLoader.h b/mozilla/content/base/src/nsScriptLoader.h
index 5f3efc71c94..58d855675b4 100644
--- a/mozilla/content/base/src/nsScriptLoader.h
+++ b/mozilla/content/base/src/nsScriptLoader.h
@@ -47,6 +47,8 @@
 #include "nsIScriptElement.h"
 #include "nsIURI.h"
 #include "nsCOMArray.h"
+#include "nsTArray.h"
+#include "nsAutoPtr.h"
 #include "nsIDocument.h"
 #include "nsIStreamLoader.h"
 
@@ -202,11 +204,26 @@ protected:
    */
   virtual void ProcessPendingRequestsAsync();
 
-  PRBool ReadyToExecuteScripts()
+  /**
+   * If true, the loader is ready to execute scripts, and so are all its
+   * ancestors.  If the loader itself is ready but some ancestor is not, this
+   * function will add an execute blocker and ask the ancestor to remove it
+   * once it becomes ready.
+   */
+  PRBool ReadyToExecuteScripts();
+
+  /**
+   * Return whether just this loader is ready to execute scripts.
+   */
+  PRBool SelfReadyToExecuteScripts()
   {
     return mEnabled && !mBlockerCount;
   }
 
+  PRBool AddPendingChildLoader(nsScriptLoader* aChild) {
+    return mPendingChildLoaders.AppendElement(aChild) != nsnull;
+  }
+  
   nsresult ProcessRequest(nsScriptLoadRequest* aRequest);
   void FireScriptAvailable(nsresult aResult,
                            nsScriptLoadRequest* aRequest);
@@ -225,6 +242,8 @@ protected:
   nsCOMArray<nsIScriptLoaderObserver> mObservers;
   nsCOMArray<nsScriptLoadRequest> mPendingRequests;
   nsCOMPtr<nsIScriptElement> mCurrentScript;
+  // XXXbz do we want to cycle-collect these or something?  Not sure.
+  nsTArray< nsRefPtr<nsScriptLoader> > mPendingChildLoaders;
   PRUint32 mBlockerCount;
   PRPackedBool mEnabled;
   PRPackedBool mHadPendingScripts;