Opens the currently playing song in Spotify
How it works:
If you're on Songza.com, a small Spotify icon appears in the omnibar and when you click on it, it opens a popup showing all the matching songs on Spotify! Artist, album, title, even the cover!
And the best: one click opens the artist/album/track page on Spotify in a new browser tab and in Spotify, so all you have to do is add it to a playlist.