diff --git a/mozilla/js/src/xpconnect/src/xpcprivate.h b/mozilla/js/src/xpconnect/src/xpcprivate.h
index dbfdbdc70fa..54fc9c33c73 100644
--- a/mozilla/js/src/xpconnect/src/xpcprivate.h
+++ b/mozilla/js/src/xpconnect/src/xpcprivate.h
@@ -2515,6 +2515,7 @@ private:
 
     static void BuildAndThrowException(JSContext* cx, nsresult rv, const char* sz);
     static JSBool ThrowExceptionObject(JSContext* cx, nsIException* e);
+    static JSBool CheckForPendingException(nsresult result, XPCCallContext &ccx);
 
 private:
     static JSBool sVerbose;
diff --git a/mozilla/js/src/xpconnect/src/xpcthrower.cpp b/mozilla/js/src/xpconnect/src/xpcthrower.cpp
index a00da11b889..a33163dc154 100644
--- a/mozilla/js/src/xpconnect/src/xpcthrower.cpp
+++ b/mozilla/js/src/xpconnect/src/xpcthrower.cpp
@@ -49,11 +49,41 @@ void
 XPCThrower::Throw(nsresult rv, JSContext* cx)
 {
     const char* format;
+    if(JS_IsExceptionPending(cx))
+        return;
     if(!nsXPCException::NameAndFormatForNSResult(rv, nsnull, &format))
         format = "";
     BuildAndThrowException(cx, rv, format);
 }
 
+/*
+ * If there has already been an exception thrown, see if we're throwing the
+ * same sort of exception, and if we are, don't clobber the old one. ccx
+ * should be the current call context.
+ */
+// static
+JSBool
+XPCThrower::CheckForPendingException(nsresult result, XPCCallContext &ccx)
+{
+    nsXPConnect* xpc = nsXPConnect::GetXPConnect();
+    if(!xpc)
+        return JS_FALSE;
+
+    nsCOMPtr<nsIException> e;
+    xpc->GetPendingException(getter_AddRefs(e));
+    if(!e)
+        return JS_FALSE;
+    xpc->SetPendingException(nsnull);
+
+    nsresult e_result;
+    if(NS_FAILED(e->GetResult(&e_result)) || e_result != result)
+        return JS_FALSE;
+
+    if(!ThrowExceptionObject(ccx, e))
+        JS_ReportOutOfMemory(ccx);
+    return JS_TRUE;
+}
+
 // static
 void
 XPCThrower::Throw(nsresult rv, XPCCallContext& ccx)
@@ -61,6 +91,9 @@ XPCThrower::Throw(nsresult rv, XPCCallContext& ccx)
     char* sz;
     const char* format;
 
+    if(CheckForPendingException(rv, ccx))
+        return;
+
     if(!nsXPCException::NameAndFormatForNSResult(rv, nsnull, &format))
         format = "";
 
@@ -91,24 +124,8 @@ XPCThrower::ThrowBadResult(nsresult rv, nsresult result, XPCCallContext& ccx)
     *  call. So we'll just throw that exception into our JS.
     */
 
-    nsXPConnect* xpc = nsXPConnect::GetXPConnect();
-    if(xpc)
-    {
-        nsCOMPtr<nsIException> e;
-        xpc->GetPendingException(getter_AddRefs(e));
-        if(e)
-        {
-            xpc->SetPendingException(nsnull);
-
-            nsresult e_result;
-            if(NS_SUCCEEDED(e->GetResult(&e_result)) && e_result == result)
-            {
-                if(!ThrowExceptionObject(ccx, e))
-                    JS_ReportOutOfMemory(ccx);
-                return;
-            }
-        }
-    }
+    if(CheckForPendingException(result, ccx))
+        return;
 
     // else...
 
diff --git a/mozilla/js/src/xpconnect/src/xpcwrappednative.cpp b/mozilla/js/src/xpconnect/src/xpcwrappednative.cpp
index 9f4d2ae038e..4e61e0312d1 100644
--- a/mozilla/js/src/xpconnect/src/xpcwrappednative.cpp
+++ b/mozilla/js/src/xpconnect/src/xpcwrappednative.cpp
@@ -461,8 +461,10 @@ XPCWrappedNative::GetNewOrUsed(XPCCallContext& ccx,
         XPCNativeScriptableInfo* si = wrapper->GetScriptableInfo();
         if(si && si->GetFlags().WantPostCreate())
         {
-            si->GetCallback()->
-                PostCreate(wrapper, ccx, wrapper->GetFlatJSObject());
+            rv = si->GetCallback()->
+                     PostCreate(wrapper, ccx, wrapper->GetFlatJSObject());
+            if(NS_FAILED(rv))
+                return rv;
         }
     }