This causes test failures once we xpconnect eating those exceptions.

Comment on attachment 801972 [details] [diff] [review] findElementWithViewId can throw if it finds nothing, so be careful to catch that exception. Review of attachment 801972 [details] [diff] [review]: ----------------------------------------------------------------- ::: browser/metro/base/content/apzc.js @@ +57,3 @@ > windowUtils.setDisplayPortForElement(0, 0, ContentAreaObserver.width, > ContentAreaObserver.height, > + element); Doesn't windowUtils.setDisplayPortFor uElement also throw if passed in an undefined element?

Comment on attachment 801972 [details] [diff] [review] findElementWithViewId can throw if it finds nothing, so be careful to catch that exception. It would if that actually happened, sure. But findElementWithViewId will never return a null element if the passed-in id is 1. So in this case, if we didn't throw an exception and break we know we have an actual element.

Comment on attachment 801972 [details] [diff] [review] findElementWithViewId can throw if it finds nothing, so be careful to catch that exception. Review of attachment 801972 [details] [diff] [review]: ----------------------------------------------------------------- r+ given that the root element will always implement nsIDOMElement and so findElementWithViewId won't return undefined.