If you use GWT with Firefox, I'd recommend delaying upgrading to the latest version of Firefox. As this article points out, if you upgrade to Firefox 3.6, the GWT developer plugin for Firefox will stop working.
I just upgraded to the dev version of Firefox, which was recommended/required to get the GWT 2.0 plugin to work. Chrome is crashing on me constantly, and my GWT apps won't run in it without disconnecting from the server.
I've reverted to IE8, which is running things properly. I think this is the first time in five years the IE has been my primary browser for development and testing.
I did something similar, I upgraded to Firefox 3.6, then reverted to 3.5. Not a big deal really. I suppose its too much to expect plugins to be immediately available in new versions of Firefox, but the harmless enough I didn't have consider reverting to... IE.