I've been complaining about Firefox being slow on a Mac for years, and all this time I should have been using Neil Lee's Mac-optimized build. The speed increase is noticeable and welcome. Downsides: The form widgets aren't identical to the original Firefox (though not bad), the app name and logo are different due to Mozilla Foundation rules (don't use the official logo on unofficial builds), and you have to get it from some dude's web site instead of a more official source. Totally worth it.