you are forgettinng ABP (ad block plus) - or sometyhing of similar ilk. Firefox does not have a host file like IE - it handles that function differently, which still leaves the threaty of some Vundorful little ass virus getting to your pc.
I test for Mozilla, now running 'Gran Paradiso" as they ceased 'Minefield'- ABP as well as themes (most), the sidebar, piclens (oooh, ahhh) and a fewrandom others. All work well, and HOLY SMOKES EVEN AS A TESTER FIREFOX IS RELENTLESSLY EASY AND PREDICTABLE.
bOTTOM LINE, ie 7 & 8 ONLY try TO FUNCTION LIKE fIREFOX, YET THEY CAN ONLY BE CHEAP, POOIRLY FUNCTIONING CLONES...
Good example: have both- open http://torrent-finder.net 1st in IE, time how long it takes to load, then try in Firefox... I do say i nare shat myself in seeing the diff. My connection is 15meg, my PC is standard Dell Toaster w/select upggrades, and I HATE AOL AND ALL ITS MEMBERS, so you know MY advice is solid gold.