Firefox's performance has improved a lot and that's really impressive. I tried moving back to Firefox but in the end I just prefer the Chrome UI too much. Using a custom search engine on Chrome can be just a matter of a couple of key presses after opening a new tab whereas in firefox I'm either stuck holding down alt and using the arrow keys or switching to my mouse. And adding new search engines is super easy in Chrome as well.

EDIT: Oh, and there was also having my browser UI lock up when a page had a misbehaving script but that might have been due to an older version of firefox.