I downloaded FireFox release candidate 3.5RC1 build2 for win32 and installed Firebug 1.4Xb2, then ran our FBTests. 424 pass, 1 fail (net/1764). More important, this version does not crash if you hit a breakpoint and put your mouse on the Script panel. Looks like that problem is behind us.
To get this version, install Firefox 3.5b4 and then immediately use Firefox > Help > CheckForUpdates and the RC1 will be installed.