Rated 5 out of 5 stars
Works quite well for me (in Firefox 3.6 and TB 3.0.4). Sometimes I wish the save breakpoints / save watch / window layout settings would be a little more persistent, and also some easier UI driven settings for window sets (instead of having to look up the command line syntax), but all in all a useful tool. Drag and drop for watch expressions would be awesome!
Beats looking up the error console by far!