I tried IceCat, but the code is horribly behind the actual Firefox releases.
Firefox is at 6.02 right now and IceCat is stuck at 5. This is a serious
problem especially on the Firefox rapid release cycle and important security
issues only get patched in new releases. The DigiNotar SSL certificate
vulnerability comes to mind.
I took a look at http://packages.trisquel.info/search?keywords=firefox and
noticed that Firefox "is" part of the Trisquel packages (even if not updated)
so I simply did a sudo add-apt-repository ppa:mozillateam/firefox-stable for
releases pre-Dagda.
I noticed that Dagda, based off of 11.04, has "abrowser" which is Firefox
anyways just without the branding. Canonical has been keeping up to date with
Firefox as of 11.04 (Dagda) and onwards so you either have to rely on the
Trisquel team keeping "abrowser" up to date or simply add the official natty
repositories in your sources.list.