This story appeared on xlr8yourmac.com, but I thought I'd repost it here too. You can now download a version of Firefox 1.0.1 compiled using G5-specific optimisations from http://homepage.mac.com/thenonsuch/firefox/. I'm currently using it to post this message on my 1.6GHz PowerMac G5. It's definitely faster than Safari, but I honestly haven't used regular Firefox on OS X enough to make a good comparison. Regular Firefox/G5 owners might like to take a look and see if there is any significant improvement to be gained by using G5-specific compilation options.