A good splitscreen view for firefox

I've been trying to use the Split browser firefox plugin It seemed to work ok. But then firefox started crashing. Thinking it may be a plugin conflict, I disabled all other plugins (except firebug). It still kept crashing. If it can't work with firebug it makes it pretty useless for trying to compare html pages and find source differences. Hopefully, I'll find a way to get it to work - or a better plugin for the purpose.