I’ve resisted Firefox, especially for This Old PC and older ones, because it’s more resource-heavy than IE. It especially takes longer to load, and I’m all about quick loading. But as IE gets more and more broken, Firefox, which has a growing share of the market, is becoming a must.
So if you can run it, then do.
If only Firefox would come up with a version that ran on pre-OS X Macs, then I’d be deliriously happy.