The Ubuntu Forums Firefox Menu Extension add-on provides easy access to all the individual sections of the Ubuntu Forums along with other handy links to make your experience of using the forums more convenient.
The original software has not been maintained by the original author (Adam Smith) but I have modified and tested it on an ongoing basis to keep it up to date and it has been available in the Ubuntu Forums.
The latest add-on version - modified 2nd March 2013 - is available here: ubuntu_forums_menu-0.82-fx.xpi
Once installed, go into the Extension Preferences to add it to your Main Menu or Context bar.
Tested as working with Firefox 19.0