I am hard working to fix all Firebug memory leaks (and did fix some of them recently). What I really need is a simple scenario showing that Firebug leaks. That helps me a lot!
How am I to tell whether leaks are from Firefox or Firebug? What I know is that after a full day developing Firefox will use 800MB of RAM, and the only way to get rid of that is to close the entire process. I use Firebug heavily and I know that _something_ is leaking somewhere.
That's nice to hear! I'll take a look on how to help.
As mkopinsky points out it's sometimes hard to tell what really leaks memory.
I can tell the same thing as he, but I think it has been improved a lot lately. Sometimes I had after some time working around 1.5GB Memory usage, but this is better now.