I've been using FF since 90s, the only extension I use is AdBlock, and at work and I don't even use that and don't miss it much either. Really don't care for the extensions, just want it simple...
I've tried Opera some time ago and hated it. I tried Chrome recently and was meh, I'm just used to FF, and don't like Chrome's look and feel.
That said, I'm getting annoyed with FF 3.6. There's a thread in the Bugs-Program forum about LFS minimization and this is totally FF's fault: whoever has Vista (not sure if Win 7 is the same) can reproduce it. Just open FF and minimize it. That's it, run LFS in fullscreen mode and it will get auto switched to window mode. Restore FF or close it and everything works fine. What the heck?? And this happens with some other games, has been reported to devs as early as Jan/Feb and despite this being a fairly serious bug (interfering with other apps, wtf), nothing has been done. Another thing is that youtube videos sometimes start skipping every 10s - turned out to be related to FF saving tabs every 10s (can be modified in about:config). A developer who does periodic I/O blocking on a GUI thread playing media should be insta-fired, luckily for him/her/them it's open source... 3.6.3 has been crashing like 2-3 times a week for me too, and there are some other smaller bugs I've noticed.
Anyway, enough of the rant, I'm still using FF hoping they will fix these bugs, if not, I think I'll be switching to something else, IE8 or Chrome (despite Google becoming too nosy)...