Firefox distribution
Can you distribute a copy of the addon for the firefox addon store?
The only change that needs to be made is to replace the options stuff in the manifest with:
"options_ui": {"page": "options.html"},
Hey sorry for not responding earlier, but I do want to keep this open. I played with it a bit a few weeks ago, and it didn't immediately work for me, I think due to some difference in Firefox's implementation of the Chrome API. Hopefully, I'll be able to get back to this soon to figure out exactly what was wrong.
It should be as simple as running it as is. The only fix needed is the options thing as mentioned in the OP. You can run/build it with web-ext e.g. "web-ext run" or "web-ext build" (https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Getting_started_with_web-ext)
Someone ported it already so I switched to that.
I've just updated and released a new version which works with Firefox. I'm gonna try to get into contact with the person who uploaded their Firefox version to see if they want to use this one directly.