I was using Firefox (version 8 I think) and Internet Explorer on the same machine. The IE was for sites that Firefox couldn't display correctly. After one Firefox and add-on upgrade, the two browsers somehow seemed to interfere with each other--and with the computer itself. I finally got rid of Firefox altogether and the problems cleared right up. Now I'm sticking with IE. It doesn't have some of the nicer improvements that Firefox does, but it gets the job done, and I don't have to switch browsers because a page doesn't display properly.
Firefox official release is 9.x now but I have been using there 64 bit beta which is version 12.x now for a few years. It blows IE out of water in speed and flexibility. I run multiple windows and tabs and it handle it effortlessly and will quickly reload them after updating browser with they do almost daily with beta. Compatibility issues (and are because web sites are not using true universal HTML code) are a thing of past mostly put when it rarely occurs. BTW there is a add one that lets you run a IE tab inside FF when needed for compatibility. I will use Google Chrome over IE any day. It also has the best built in streaming support (flash and such in integrated) and will run stream video on slower machines that choke with IE or FF at times. Being that I have a 64 bit machine with 8 gigs and 4 cores HP is not a issue here. If you machine did not like them both do not blame FF but rather MS or some other app you may have because I have never seen FF cause a problem itself.