Run Firefox 3 and Firefox 2 simultaneously
Life is officially easier for front-end web developers, you can now easily test browser compatibility by running Firefox 2 and Firefox 3 concurrently with a great utility called MultiFirefox. Simply install MultiFirefox, then rename one of the Firefox applications (to say, Firefox 3), and upon launch you can select either application version to run. MultiFirefox is fast, free, and simple to use, so check it out. Mac web developers rejoice!