Rated 5 out of 5 stars
If I had to live one day without this add-on I would throw myself off a cliff. This is the best thing to happen to any browser since the back button. Any developer needs to get this add-on and use it. I am tired of seeing problems on other people's sites! This will show you everything you need to know about what is going on with your site. The only drawback is that if your site has a lot of moving parts your computer will really get bogged down. Check out FireCookie too, it's a big help if you run any corporate sites.
-Chad R. Smith