I've been a Mozilla user, and when i heard about Firebird i jumped at the chance to try it.
I used it once, but the one thing that turned me off the most is when you right click the tabs for each window, the close tab option is at the bottom, as opposed to the top in Mozilla.
So i ran away.
I love the lack of installation of it though. A little freaky at first, but very satisfying when you realize that it actually works.
I'll go back to it, but not just yet. I promise