gistfile1.diff

diff --git a/js/src/xpconnect/src/xpcthrower.cpp b/js/src/xpconnect/src/xpcthrower.cpp
--- a/js/src/xpconnect/src/xpcthrower.cpp
+++ b/js/src/xpconnect/src/xpcthrower.cpp
@@ -257,16 +257,18 @@ XPCThrower::BuildAndThrowException(JSCon
     // most likely out of memory 
     if(!success)
         JS_ReportOutOfMemory(cx);
 }
 
 static PRBool
 IsCallerChrome()
 {
+    NS_ASSERTION(NS_IsMainThread(),
+      "Acessing security manager off main thread.");
     PRBool isChrome = PR_FALSE;
     nsCOMPtr<nsIScriptSecurityManager> securityManager =
         do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID);
     nsresult rv = securityManager->SubjectPrincipalIsSystem(&isChrome);
     return NS_SUCCEEDED(rv) && isChrome;
 }
 
 // static
@@ -278,17 +280,19 @@ XPCThrower::ThrowExceptionObject(JSConte
     {
         nsCOMPtr<nsXPCException> xpcEx;
         jsval thrown;
         nsXPConnect* xpc;
 
         // If we stored the original thrown JS value in the exception
         // (see XPCConvert::ConstructException) and we are in a web
         // context (i.e., not chrome), rethrow the original value.
-        if((xpcEx = do_QueryInterface(e)) &&
+        if(XPCPerThreadData::IsMainThread(cx) &&
+           NS_IsMainThread() && // redundant?
+           (xpcEx = do_QueryInterface(e)) &&
            xpcEx->StealThrownJSVal(&thrown) &&
            !IsCallerChrome())
         {
             JS_SetPendingException(cx, thrown);
             success = JS_TRUE;
         }
         else if((xpc = nsXPConnect::GetXPConnect()))
         {