And Piro didn't stop with Tabbrowser Extensions! He's got projects even cooler than that. Check out his ContextMenu Extensions. This is not your average end-user fare but for all of us that really use the Web it's great. It adds so many features that I can't begin to list them here. Go read about them in the ContextMenu Extensions help file (thanks again for the English translation, Piro. Your English is great) or install the XPI and see for yourself. I haven't been playing with it for long but so far I really like it, especially the stylesheet menu with it's user stylesheet editor.
