That's what I've done, but I see 2 of them.
I've tried to disable all other extensions in FF, except Firebug, same result.
I've than reinstalled the version 1.11.4, same effect.
But after installing the 1.10.6 it works!
When i try to upgrade to 1.11 again, i get the same problem, so i will now use the 1.10.
I'm using FF 22 on OSX 10.8.4.
So for me it looks like 1.11 has a problem.