The one thing that has given me more problems than anything with browsers is Flash. I've lost count of the number of times that a browser tab will shoot up to 90+ percent cpu due to Flash content. Unfortunately, so many websites require Flash for content, instead of it being gravy. I'm running XP 64, and have used a 64 bit build of Firefox that is amazingly fast compared to the regular version. The problem is addons like Flash, 64 bit version doesn't exist yet.