Fire.fm Firefox Add-on
Fire.fm is a direct access to the extensive music library on Last.fm. Listen to music related to your favorite artist or genre, and discover new artists and music in the process. Listen to your friends' favorite music. Find Last.fm users with musical taste similar to your own. Quickly access your favorite stations by just typing a few letters into the location bar. This is the ultimate add-on for the music junkie.
https://addons.mozilla.org/en-US/firefox/addon/7684
There are some pretty good reviews there, so you don't have to take my word for it ;). I'm one of the developers of Fire.fm, BTW. There's more information at our site:
We hope you like it!
Jorge