Following on from BigC's blog post, Ubuntu users might be interested to know about a repository that contains the latest alphas and betas for Firefox.
Add the following to your repository list:
deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu jaunty main
The GPG key can be found at: http://keyserver.ubuntu.com:11371/pks/lookup?search=0xB34505EA326FEAEA07E3618DEF4186FE247510BE&op=index
I've installed both 3.5 and 3.6 alongside my existing 3.0.11 and they run fine. Neither has actually crashed on me either.