Obviously i love greasemonkey, one of the best ever extensions of firefox. Here is perhaps the best ever.
firebug from mozilla or from firebug website
What does it do?
Install firebug just as you install all other extensions.
Enable firebug. (press F12 and click enable firebug), Alternatively, you may also use Tools-> Firebug -> Enable firebug
Now visit your website […]
