I wouldn't say Firefox is slow, but the UI still has weird latency issues that I don't see in Chrome.
For the record, I use both Chrome and Firefox, heavily. The Chrome UI is very rarely laggy. The Firefox UI is often laggy. It's maddening, and I wish Mozilla would fix it.
I find this true, and I've been an old Firefox user. Stopped for a while after a bunch of issues after 4, and after that I've been off and on really TRYING!, but nah.. sticking with Chrome.
Not always worth the effort of switching back and forth. I stopped using FF when it was a slow memory hog. I've heard good things about it recently, but I have no real incentive to switch back.