NoScript
https://addons.mozilla.org/en-US/firefox/addon/722
The best security you can get in a web browser!
ShowIP
https://addons.mozilla.org/en-US/firefox/addon/590
Show the IP address(es) of the current page in the status bar.
SeoQuake
https://addons.mozilla.org/en-US/firefox/addon/3036
Seoquake is a Mozilla Firefox SEO extension aimed primarily at helping web masters who deal with search engine optimization(SEO) and internet promotion of web sites.
Live PageRank
https://addons.mozilla.org/en-US/firefox/addon/2007
Display PageRank for active URL.
Screengrab
https://addons.mozilla.org/en-US/firefox/addon/1146
It will capture what you can see in the window, the entire page, just a selection, a particular frame... basically it saves webpages as images - either to a file, or to the clipboard.
JSView
https://addons.mozilla.org/en-US/firefox/addon/2076
All browsers include a "View Source" option, but none of them offer the ability to view the source code of external files. Most websites store their javascripts and style sheets in external files and then link to them within a web page's.
B.