Here is a great post on how can you expand your Firefox reading experience.
Plain text to link: turn any highlighted text into a link
Browse pages tagged with this word / phrase on StumbleUpon
Count the highlighted words: word count plus
Search the highlighted word in any search engine you select in your search plugins
Search the highlighted word using multiple search engines: KallOut
Search the highlighted word using Google advanced operators – advanced dork
Written by Vygantas Lipskas on December 28, 2008