--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -2162,33 +2162,37 @@ nsGlobalWindow::SetDocShell(nsIDocShell*
       // Remember the document's principal.
       mDocumentPrincipal = mDoc->NodePrincipal();
 
       // Release our document reference
       mDocument = nsnull;
       mDoc = nsnull;
     }
 
-    mContext->ClearScope(mJSObject, PR_TRUE);
+    if (mContext) {
+      mContext->ClearScope(mJSObject, PR_TRUE);
+    }
 
     ClearControllers();
 
     mChromeEventHandler = nsnull; // force release now
 
     if (mArguments) { 
       // We got no new document after someone called
       // SetArguments(), drop our reference to the arguments.
       mArguments = nsnull;
       mArgumentsLast = nsnull;
       mArgumentsOrigin = nsnull;
     }
 
-    mContext->GC();
-    mContext->FinalizeContext();
-    mContext = nsnull;
+    if (mContext) {
+      mContext->GC();
+      mContext->FinalizeContext();
+      mContext = nsnull;
+    }
 
 #ifdef DEBUG
     nsCycleCollector_DEBUG_shouldBeFreed(mContext);
     nsCycleCollector_DEBUG_shouldBeFreed(static_cast<nsIScriptGlobalObject*>(this));
 #endif
   }
 
   mDocShell = aDocShell;        // Weak Reference