Add publish-firefox-extension to CI workflow

[HarlemSquirrel]

Use https://github.com/marketplace/actions/firefox-addon-action to publish the extension to Firefox addons in the CI workflow.

Before we can test this we need to

• set two secrets FIREFOX_API_KEY and FIREFOX_API_SECRET.
• get or set the guid. See https://mozilla.github.io/addons-server/topics/api/addons.html#put-create-or-edit

[HarlemSquirrel]

@antelle I'm unable to publish the extension myself.

Your add-on failed validation with 1 error.
Duplicate add-on ID found.

Can you add me as an author? My email for my Firefox account is [email protected]
https://extensionworkshop.com/documentation/publish/add-on-ownership/

[antelle]

I wonder how. My Firefox account with that extension is deleted, so I can’t anymore

[antelle]

[HarlemSquirrel]

Oh fun, sounds like we may need to change the ID of the extension.

[HarlemSquirrel]

Secrets are not shared with PRs from forks 🤦 so opening a new PR