with the new Ubuntu came Firefox beta 3, then the Firefox final 3 but Firebug just didn’t work
FYI Firebug is a great web development add on for Firefox
now after like a month or two 
I found a way to make it working
just remove the Firebug extension if you have it that does not work
and then install Firebug from the packages
I used the command line
aptitude install firebug
have fun 