I used to have this problem for a while on lucid. There was also a bug submitted to firebug (firefox crashed with firebug installed). Going to a newer version of firefox/firebug solved the problem at the time.
I had no problems so far with firebug on amd64 using Maverick (10.10).
Maybe you need to be more specific what the exact issue is, if this will not help.
I used to have this problem for a while on lucid. There was also a bug submitted to firebug (firefox crashed with firebug installed). Going to a newer version of firefox/firebug solved the problem at the time.
I had no problems so far with firebug on amd64 using Maverick (10.10).
Maybe you need to be more specific what the exact issue is, if this will not help.
Firebug plugin works fine in Ubuntu 10.10 64 bit. I am using it without any issues on Firefox 3.6.12.