I'm considering switching for a few cosmetic issues (against Chrome):
1. I continued to be annoyed by Chrome's weird "close a tab with the middle mouse button" feature
2. Bookmark management in Chrome kind of sucks
3. The minimalistic UI is getting out of hand. Having the menu in that little "wrench" icon is a bit annoying
4. The settings dialog sucks, specially the proxy settings (they reuse the IE dialog which looks clunky).
5. The auto update feature in Chrome just doesn't work for me (might be our firewall)
The problem with Firefox is that I ran an HTML 5 compatibility test and Chrome still scores higher than it.
Still using Chrome, but might be time to try Firefox again (The tabs in firefox are a bit ugly, please make them more curved!)