This add-on shows now playing notifications for soundcloud and bandcamp and allows you to scrobble songs to Last.fm, love/unlove them, and search current artist or track using a shortcut in google. Fully customizable via preferences.
Here is more information about the Webscrobbler add-on for Firefox:
The addon will open a tab on last.fm asking you to give it permissions to scrobble the songs you listen to using soundcloud and bancamp. You can disable scrobbling per site (soundcloud and bandcamp), disable notifications and configure the time interval in seconds the now playing notifications are shown.
Want to learn more? You can pick up this add-on and learn more about it on the Firefox Add-ons website.