Firefox sucks
I've been running Firefox 3.1/3.5betas since last year. Only since Beta4 (3.5b99) and now with every release candidate since - including the last one - has problem come up: I lose all Internet connectivity in all tabs regularly. Other browsers & internet-connected apps still work, but Firefox has lost it. I have to close Firefox and restart. What a joke!
Also, don't call Firefox fast: it takes at least THIRTY SECONDS on a new, speedy machine running XP to initially start the browser. That's ridiculous!