Honestly, my issue with Firefox all comes back to the Omnibar: I just like how Google does it better. And the only Firefox plugin I've seen that gets similar to that behavior, is slower at every step of the way. Also, having to manually add every search engine is a hassle even if you are willing to put up with the extra steps that plugin asks.
I really like Google, but I want to support open source(and am not quite willing to put up with Chromium). But for me, core usability is still king, and nothing really touches Chrome for that.