some useful firefox plugins :
Adblock (alternate link)
The Adblock extension can strip nearly every kind of ad out of web pages, including Flash and Java applets, as well as help prevent pop-ups.
DownThemAll (alternate link)
DownThemAll makes it easy to download all links or images on a page in one shot.
FireBug (alternate link)
FireBug is an integrated JavaScript, CSS, HTML, and Ajax debugger for Firefox, including an error console, command line, and inspectors
Page Recolorization (alternate link)
- Modifies color scheme of current page to ease readability
FORM Help> (alternate link)
- Shows hidden form fields and enables disabled and read-only fields