I have tried FireBird in the past but I've always gone back to Mozilla. I decided to give a shot to FireFox. I'm very pleased with it.
It finally handles mailto links. Not just that, but lets you choose the email client of your choice.
It let's you open wmv files with mplayer (or any other video player) even if the mime-type is not set up correctly on the web page. This was a major pain in Mozilla.
A few minor quirks though. Had to dig hard to find where to check for installed plug-ins. It did not show mplayerplug-in, even though it was installed and working. It stores user data in ~/.phoenix, it would make more sense to have it in ~/.firefox.
Anyway, it became my default browser really quick.