Set up semantic release for Firefox

[wkillerud]

• [x] Submit add-on to https://addons.mozilla.org/
• [x] Get it approved
• [x] Configure https://github.com/tophat/semantic-release-firefox-add-on
• [x] Test the automated release pipeline

[wkillerud]

Needed a patch and an unexpected path config for the semantic release plugin, but it's working!