All the useful add-ons for search engine marketers (SEM).
Protect your privacy. See who's tracking your web browsing and block them with Ghostery.
FireShot Webpage Screenshots captures webpage screenshot entirely (see demo: http://bit.ly/RlBQMV)
The screenshot can be quickly annotated and:
+ Saved as PDF/PNG/GIF/JPEG/BMP
+ Sent to clipboard
View HTTP headers of a page and while browsing.
SEO Global For Google Search™ (Formerly Google Global) is an unobtrusive Firefox extension that allows you to see what the Google search results that you are viewing look like from different geographical locations.
KGen (Keyword Generator) allows you to see what keywords are strong on visited web pages for search engines.