Lets put it this way. If you like insecurity, go for IE If you like being safe on the internet, then go firefox Its all preference really
I don't find Firefox slow, it's just when opeing the program it's slow, other than that i have no other problem with it ^_^
Firefox is a bigger program, so it takes longer to load, and could quite possibly slow up your computer and make the images load slow. But if you have a supercomputer, It shouldn't make any difference.
Don't use firefox or IE download realplayer wich comes with a browser I everything loads faster than firefox, and has sort of a pop-up blocker. The movies look better and the sound is awesome. Get realplayer 10 (free version not the trial).
My firefox runs slightly slower but ive been using it for so long that i cant really remember what it was like on internet explorer. It does load images slow like all the banners in sigs on this site, but with a good connection speed its not really any problem.