As another Extend Firefox 3 contest winner, HandyTag deserves a look. This add-on for Firefox provides a complete set of the most relevant keywords when you bookmark a page. Where do these keywords come from? Many different sources from around the Web.
This comes in handy when you bookmark a page, and your not sure exactly with what words it should be tagged with (or you don’t want to take the time to think it out). There is no need for straining your brain to think of descriptive tags any longer with this extension.