I have gone back to chrome, just prefer the minimal UI, the way the add ons work on chrome, faster overall as well, although I think firefox renders the web pages quicker.
One thing, which I did love about FF 4 was the hardware acceleration thing or whatever it was, it was so smooth scrolling down web pages, especially the "high res screenshot thread" compared to chrome, hopefully chrome will get that part done as good as what mozilla has.
Didn't care too much about the grouping tabs things, although I can see how it would be very useful for some people, also its nice to see that they have got the pin tab feature as well.