For you those don't understand how to use it, this addon allows you to control Google Play Music from any tab in your browser.
This only works for Google Play Music (as far as I know), which is at play.google.com/music
There's three simple shortcuts. These are all keyboard shortcuts.
To pause the currently playing music, or continue the paused music press:
CTRL ALT P
That's the CTRL key, plus the ALT key (both located in the bottom left of your keyboard), then the P key, as in the letter p!
This also applies to the other shortcuts like next song and previous song. The only difference is that to skip a song, press the PERIOD key ( . ) That's located just above and a little to the right of the space bar.
To go to the previous song, just use the same combination (CTRL + ALT), but this time, press the COMMA key ( , ) located above the right end of the space bar.