I use a tabbed IE based browser called Slimbrowser it's pretty good.
The Tabs are hella useful.
Plus the pop-up blocker on it is awesome (Ya know those annoying adverts you get that are like "Shoot the ipod to claim a free one" and you feel like you have to shoot the Ipod, the browser blocks the pages that open because of the adverts

Which means I can shoot away heh. I don't know if firefox does this though, 'cause I don't have it...)
It's pretty fast (better then IE by far) and loads initially pretty fast.
I'm not sure how customisable it is (I've only been using it for a week and I'm lazy :-])
I can't compare to FF though, 'cause I don't use FF often enough.
http://www.flashpeak.com/sbrowser">FlashPeak SlimBrowser