Rated 5 out of 5 stars

GM is the single most useful add-on for Firefox. Nothing else even comes close to the flexibility and feature range it offers. Rather than modifying the browser, GM directly interacts with websites to add, remove, or entirely alter how those sites perform. As an example, the "SocialFixer" script changes Facebook (for the better) to the point that it's almost unrecognizable from the original. Greasemonkey makes possible what no other add-on even dreams of. It's so flexible, it actually has a site, userscripts.org, to search and install web page scripts.

This review is for a previous version of the add-on (0.9.18).