Rated 4 out of 5 stars
I must agree with others. It's quite simple add-on, but very useful and surprisingly stable. I use it from Nightly 12 or 11 and only once there was a problem: it stuck for one profile, reset settings each time I opened Nightly. But it was fixed very quickly. From then no more problems.
I think it's a real shame that Firefox doesn't have such feature by default.
Thanks for great job, Paolo!