GrooveShredder

If you usually listen to music using that outstanding online service called Grooveshark, you'll welcome this add-on for Firefox.

GrooveShredder will change the play button for a download button, so you'll only have to search for any track in Grooveshark and play it. When you'll click the play button, it will be downloaded automatically.

Of course, if you want Grooveshark to work as usual you'll only have to disable the add-on.