Here is a FIX for the new Material design Rated 5 out of 5 stars

Just replace line 34 in the main.js file in the extension with the following:
contentScript: "(document.getElementsByClassName('material-player-middle')[0].childNodes[" + act + "]).click();"

Cheers :)

This review is for a previous version of the add-on (0.7.1-signed). 

new version available

thanks for your help bringing this to my attention. You can add a new version of this addon from here: https://addons.mozilla.org/en-US/firefox/addon/google-music-hotkeys/versions/?page=1#version-0.8

Lost functionality Rated 5 out of 5 stars

This addon fails to control Google Music after recent Material redesign.

UPDATE. Everything is back to great after update. Cheers.

This review is for a previous version of the add-on (0.7.1-signed).  This user has a previous review of this add-on.

New version available

thanks for your help bringing this to my attention. You can add a new version of this addon from here: https://addons.mozilla.org/en-US/firefox/addon/google-music-hotkeys/versions/?page=1#version-0.8

Awesome Rated 5 out of 5 stars

If you want to collaborate, I made another add-on similar to this one.

It's not a big thing, but it's working. Also, you can customize the hotkeys :
https://addons.mozilla.org/en-US/firefox/addon/google-music-control/

This review is for a previous version of the add-on (0.7.1-signed). 

Thanks! I'm not sure how you want to collaborate since we are both doing such similar things, but if you have any particular ideas let me know.

Rated 4 out of 5 stars

Nice addon, however Play/Pause shortcut ctrl+alt+p doesn't work for me. Next and Prev are functional.

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 5 out of 5 stars

Works as described, scratches a big itch!

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 4 out of 5 stars

I would like to collaborate in the development of the addon. I would like to make hotkeys customizable.

This review is for a previous version of the add-on (0.7.1-signed). 

I would gladly welcome your help. What is the best way to get in touch with you so we can coordinate?

Firefox 30.0, Windows 8.1 x64 Rated 4 out of 5 stars

Extension works OK. Please add like/dislike and support of hardware multimedia keys.

This review is for a previous version of the add-on (0.7.1-signed). 

Needs 2 hands but works! Rated 4 out of 5 stars

They're not the hotkeys I would have picked but the addon works perfectly. I'd have preferred to set my own hotkeys - I would have picked something like CTRL-ALT-W which I could input with one hand.

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 5 out of 5 stars

Almost perfect. This plus AutoHotKey to switch focus back and forth gives me global media keys. Finally.

This review is for a previous version of the add-on (0.7.1-signed). 

Thank you for this Rated 5 out of 5 stars

I had almost given up being able to control Google Music with the keyboard. This works really well.

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 5 out of 5 stars

OMG, thank you! Hate that there's no desktop client, and Chrome hiccups the music too much. You saved my subscription.

Please add a hotkey for searching google music. Thanks!

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 5 out of 5 stars

I thought "hey, there should totally be an extension that does this," and here it was. No restart, 5 seconds later I'm pausing and unpausing my music like a pro.

This review is for a previous version of the add-on (0.7.1-signed). 

Rated 5 out of 5 stars

Any update on the prev/next keys not working? Would be really fantastic if you could fix this.

Edit: fixed, thank you!

This review is for a previous version of the add-on (0.6.1-signed). 

I have updated this to version 0.7 :

https://addons.mozilla.org/en-US/developers/addon/google-music-hotkeys/versions/1504714

which should re-enable the next/prev functionality.

Stopped working. Rated 1 out of 5 stars

The "Next" & "Prev" buttons no longer work :(

This review is for a previous version of the add-on (0.6.1-signed).  This user has a previous review of this add-on.

I have updated this to version 0.7 :

https://addons.mozilla.org/en-US/developers/addon/google-music-hotkeys/versions/1504714

which should re-enable the next/prev functionality.

Great addon - and how to make it work with system-wide shortcuts (Linux) Rated 4 out of 5 stars

Love this - but not a fan of the shortcut combos - nor the fact that they aren't global.

To fix this, simply map your favourite key-shortcut to the following commands:
Next track: xdotool key --clearmodifiers --window `(xdotool search --classname Navigator | head -1)` ctrl+alt+period
Previous track: Next track: xdotool key --clearmodifiers --window `(xdotool search --classname Navigator | head -1)` ctrl+alt+,
Play/Pause: Next track: xdotool key --clearmodifiers --window `(xdotool search --classname Navigator | head -1)` ctrl+alt+p

If you're using KDE:
1. From system settings choose "Shortcuts and Gestures"
2. Under "custom shortcuts" choose Edit->New->Global shortcut->Command/URL
3. Give your shortcut a nice name and comment (optional)
4. Under the Trigger tab, select the keycombo you'd like to use. I suggest using Ctrl with your media keys
5. Under Action, enter the appropriate command (as given above)
6. Repeat steps 2-5 for the other two commands given above.

This review is for a previous version of the add-on (0.6.1-signed). 

Rated 3 out of 5 stars

Great addon, would be great if the keys were global throughout the OS

This review is for a previous version of the add-on (0.6.1-signed). 

Works great Rated 5 out of 5 stars

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.

This review is for a previous version of the add-on (0.5.1-signed). 

Works as designed :) Rated 5 out of 5 stars

Does exactly what it says, works as intended.

The standard improvements would be cool:
- Customizable keys
- thumbs up/down for the current track
- volume up/down

This review is for a previous version of the add-on (0.5.1-signed). 

Thanks a LOT!!! <3 Rated 5 out of 5 stars

Superb stuff! Just what I needed! And works perfectly!

This review is for a previous version of the add-on (0.5.1-signed). 

Rated 1 out of 5 stars

Unfortunately, the instructions are vague. Please write appropriate instructions.

This review is for a previous version of the add-on (0.5.1-signed).