Custom shortcuts don't work on macOS

[SynVisions]

macOS 10.12.6
Firefox Quantum 66.0.3 (64-bit)

Even with the default shortcuts, they don't work, even when the Google Play Music tab is in focus.

Clicking on the toolbar button for the extension does the appropriate play/pause, so that part of the code is working at least. Shortcuts don't work at all for me.

[SynVisions]

Ok, I ran the extension in debug mode which fixed the problem with the default shortcuts (no idea why), but the ones I want to use aren't working. Seems like they aren't translating to the right thing.

I'm now seeing this mapping happen when I close and reload the extension after setting my options.

Space -> MacSpace
Right -> MacRight
Left -> MacLeft

Similar to #13 ?

[lidel]

Thank you for reporting this. Sadly I don't own a Mac and can't reproduce this.

If anyone sees this and can help a PR or a comment (even if it is "i have a mac and works for me") with will be appreciated.