I submitted the same issue a while back with 2.0 version, and the issues continues to happen:
Basically, firebug does not stop at the break points you have specified in JavaScript/JQuery code. And that is because the line numbers displayed in firebug are not in sync with the actual code.
Please see the screen shot of the problem and the description of the issue as I posted it a few months ago:
https://groups.google.com/forum/#!topic/firebug/EDHH1M_tTbYPlease HELP, as this is really severely impacting our development work (with latest version of FF not working with Firebug below 2.0 version).
Thank you,
AJ