Code changes are in SVN to run gears with Firefox 3.6, I have just compiled an installer for 64-bit linux for my own needs. This talks happily to FF3.6 (final running on opensuse 11.2).
Feel free to grab it for testing here: http://gears.googlecode.com/issues/attachment?aid=-12708196062073299&name=gears-linux-x86_64-opt-0.5.34.0.xpi
