For me, Firefox isn't any faster than Safari, at least on the pages I've tested it with. I have NOT used the appropriate optimized build for my machine. When started for the first time (ever, not the first time after a restart), Firefox launches, quits, launches, quits, launches, and displays the browser window. Safari launches, delays for 1-2 seconds while it configures itself, and displays the browser window. On subsequent launches, Firefox behaves like Safari's first launch, while Safari comes up immediately (1 bounce, then the browser window appears). Also, Firefox puts a bunch of files in your user library - not all of them are obviously associated with Firefox (the FullCircle folder in ~/Library/Application Support is a good example), whereas Safari puts its preferences in the preferences folder, its cookies in a special Cookies folder, and everything else in the Safari folder - much cleaner. This is why I prefer Safari over Firefox.