Usable, stable, just needs code to get windows Rated 2 out of 5 stars
It has a good usability, it's stable and secure as far as I can tell.
I use it without any problem with Firefox 3.6.x.
The online documentation is of a very good quality. Very useful for developers.
The only problems that block me are the impossibility to select/trap alert windows and filechooser windows. Thus I use UxU more for unit testing JSM modules and use Mozmill more for functionally testing windows.
Thanks a lot for this great extension!