One of the things I got used to very fast when starting with “firebird” (the original name of FireFox) were the tabs. Yet when you have a lot them opened, then you can easily lose track of what was what. This addon gives each tab a nice pastel color, easily identifying your tabs, and nice on the eyes.
I think this was stolen from the ideas from IE. Yet they’ve probably had stolen it from Mac… and they’ve stolen enough from Firefox in the past. So who cares? It’s a nice thing. You press F12, and you get a visual overlay of all the pages you have open.
Building websites? Then you NEED this. I cannot believe this wasn’t developed ages ago.
A crossplatform ftp client in the shape of a firefox plugin.
Choose which flash things need to be shown (thus downloaded).
Measure anything on a webpage. Handy when designing imo.