When the message manager calls JS_ExecuteScript for content scripts, it ignores errors. However, there's a problem if there was already JS on the stack when LoadFrameScriptInternal was called. In that case, the JS engine will leave an exception on the JSContext, which is just an AutoSafeJSContext. Whoever is unlucky enough to get that context next will randomly encounter that exception and fail. This patch just reports the error, which I think is good practice anyway. If you're wondering how there can be JS on the stack when LoadFrameScriptInternal is called, it happens when we're running in single-process mode. In that case, calling messageManager.loadFrameScript in JS will just run the script directly.

Comment on attachment 8360622 [details] [diff] [review] message-manager-error-fix Review of attachment 8360622 [details] [diff] [review]: ----------------------------------------------------------------- Ugh yeah. In theory, AutoSafeJSContext unconditionally pushes a JSContext, which one would think would insert a SavedFrameChain boundary, which should cause SpiderMonkey to invoke js_ReportUncaughtException at the end of the JS_CallFunctionValue call. However, there's this stupid optimization where we don't invoke JS_SaveFrameChain if the push wouldn't change the principal. So if the caller is also using an AutoSafeJSContet, they get screwed. This needs fixing in the long run, but this is fine for now. r=bholley

I started poking around in this code some more, and I couldn't stop myself from making this change. I haven't seen any other code that uses |ctx| instead of |cx| for a JSContext.

After some more debugging, I found that this was causing my second test failure (specifically the JS_CallFunctionValue, although it's easy to see how the JS_Stringify could fail too).

I pushed these to fx-team since my session restore changes rely on them and the chance of a merge conflict seems very low. https://hg.mozilla.org/integration/fx-team/rev/d020e9d743a6 https://hg.mozilla.org/integration/fx-team/rev/3dcedecd2bbf https://hg.mozilla.org/integration/fx-team/rev/2e1513b84c6c

https://hg.mozilla.org/mozilla-central/rev/d020e9d743a6 https://hg.mozilla.org/mozilla-central/rev/3dcedecd2bbf https://hg.mozilla.org/mozilla-central/rev/2e1513b84c6c