Firefox 3.0.10 is horribly slow on my system, it crashes pretty frequently on startup. I've been using the Ubuntu Chromium daily builds off of Launchpad for the past for days (https://launchpad.net/~chromium-daily/+archive/ppa), and it's really been a refreshing experience - the web is responsive again! It obviously isn't ready for release yet, but if you build that into your expectations, it's actually quite pleasurable to use.