Firefox is only useful if you are like using a bazillion extensions. If you just want speed Google Chrome whips Firefox and is just a little faster than IE8, which offers far better usability and is the official evilbore browser of now and forever.
Also, the sites that are running bad-can you tell if the scripts are ad-related? That's where I usually get hangups, outside of a few intranet apps that were obviously coded by college co-ops hopped up on goofball.