Works as expected with 0.6 update Ohodnoceno 5 z 5 hvězdiček

Everything is good again with experimental version. Thanks.

Tato recenze je pro předchozí verzi doplňku (0.5). 

Thanks for the review. I uploaded a new version, 0.6, to fix compatibility issues. Please try it out from: https://addons.mozilla.org/en-US/firefox/addon/google-music-hotkeys/versions/

Let me know if this fixes your issues.
Thanks.