Comment 4 for bug 385630

This is fallout from a pretty old change: we used to ignore any and all parsing errors in XPI files, and we don't any more. We also improved the reporting of errors in several ways since then, which is probably why the problem took so long to become visible enough.

At first glance, I'd say the fix is probably to call DTDParser.set_inputsource_factory to substitute a custom factory. That's also a first step on the way for another improvement that asac has long been waiting for.