Rated 4 out of 5 stars
This is a quite interesting and great add-on. It is able to inspect internals lots better than firebug's console..
I have been using version 1.0 since a week ago only (didn't know of his existence before), and i have to tell i love it.. However... i was about to report this version as broken until i saw your website, where it is told it's for FireFox 4.x (oh, wait, or do you only mean support for it was added, then you broke it)
Here under win32 3.6.13 does not work, clicking "Start" under Options window or Tools menu does nothing.
If it would work, i would rate it 5, i rated it 4 with version 1.0 in mind ;)
I've release a beta version to bring mozrepl on the upcoming firefox 4.0 release and tried to fix incompatibilities using "back-compatible" strategies... but it didn't work :-P
Thank you a lot for your beta-testing activity, I've fixed "Compatible Application" section in the beta release and uploaded last stable version as you are used to on firefox 3.0-3.6.*