*Update* Yesterday kaeru pointed out that firebug from the ubuntu repo works with the default firefox 3 beta on Hardy. Just tried it and I'm glad to report it does work very nicely. No more need for this workaround.. Just look for it in synaptic or apt-get install firebug.
What can I say? Ubuntu is pretty bleeding edge. :P It comes with firefox 3 beta 5 which is pretty slick. But there are still a lot of add-ons which do not work with firefox 3 beta. Earlier on I've blogged about using the 1.1 beta of firebug with firefox 3 beta. It works pretty well on my home box which runs arch linux. But on my computer at the office running on Ubuntu, firebug doesn't even come out. So I had to find a way around.
Luckily Firdaus of OSCC showed me that you actually can install Firefox 2 on Ubuntu. It's still in the repo and you just have to select it with synaptic or apt-get 'Firefox-2'. But the default installation will share the same default profile of Firefox 3 and so will break firebug when you launch Firefox 3. So what can you do? KageSenshi showed me how creating profiles for firefox will solve the problem. Well, first you have to create a different profile just for Firefox 2 by running 'firefox-2 -profilemanager'. There you can create your profile. Make sure you never use this new profile with Firefox 3 so what we do is that we change the command of the icon to start firefox 3 to 'firefox -P "Default"' and the icon to start firefox 2 to 'firefox-2 -P "firefox2"' (Use the name of the profile you created before). I don't think you can run both versions at the same time but I don't have time to experiment right now. These settings work and I have to get back to work.