Aaron Wall of SEOBook has nice tidbits to share about the essence of using Firefox in doing web search engine optimization.

SEO for Firefox Features:
Pulls useful market research data right into Google's and Yahoo!'s search results, including the following data near each search result.

PR: (Google PageRank) an estimated measure of global link authority
Age: age pulled from Archive.org, shows the first time a page was indexed by Archive.org's spider. The theory is that if Archive.org found a page so did many of the major search engines.
Links: (Yahoo! linkdomain) shows a rough estimate of the total number of links pointing at a domain
.edu Link: (Yahoo! .edu linkdomain ) shows a rough estimate of the total number of .edu links pointing at a domain
.edu Page Link: (Yahoo! .edu link ) shows a rough estimate of the total number of .edu links pointing at a specific page
.gov Link: (Yahoo! .gov linkdomain ) shows a rough estimate of the total number of .gov links pointing at a domain
Page Links: (Yahoo! link) shows a rough estimate of the total number of links pointing at a page
del.icio.us: number of times a URL has been bookmarked on Del.icio.us. Heavily skewed toward techy / Web 2.0 stuff.
Technorati: an estimate of the total number of links to a site from blogs
Alexa: rank based on website traffic . Heavily skewed toward internet marketing and webmaster related resources.
Cached: (Google site:) shows how many pages from a site are indexed in Google
dmoz: searches the Google Directory to count the total number of pages from a site that are listed in DMOZ, and the total number of pages listed in DMOZ that reference that URL.
Bloglines: shows you how many people are subscribed to a particular blog via Bloglines.
dir.yahoo.com: is a site listed in the Yahoo! Directory or not.
WhoIs: makes it easy to look up the whois data for any site.