Whenever I've encountered a problem with firefox crashing / behaving oddly or slowly it hasn't actually been firefox's fault. It's far more likely to be one of the add-ons you've got installed, the quicktime add on is a bit of a notorious one for instance and the skype one always used to cause some sites to crash firefox entirely for me (hotmail for instance.) So if you are having troubles, I'd recommend running firefox in safe mode (that's firefox's safe mode not window's!) and seeing if they're solved. If they are then disable the add-ons one by one until you find the cluprit.
Then smash it with a hammer.
I like both Chrome and firefox, but when you're developing using GWT / AJAX / javascript in general, firebug is an absolute must have. Imacros is also a great little app, and there's a few others as well. Chrome will get there - but since firefox has been around for many years longer, its add-on base is inevitably far bigger.