WebExtension manifest v3 (Firefox)

[toasted-nutbread]

Firefox is moving towards supporting MV3, using a slightly different pattern than Chrome. Firefox is supporting event pages, which should allow the background page to be maintained, which addresses some of the outages of Chrome MV3's service worker.

However, since eval is no longer allowed and Firefox doesn't support sandbox pages, this will break handlebars, so a workaround will be needed for that.

https://blog.mozilla.org/addons/2022/05/18/manifest-v3-in-firefox-recap-next-steps/
#455
#1247
#2155

[toasted-nutbread]

Sandbox support on Firefox:
https://bugzilla.mozilla.org/buglist.cgi?product=WebExtensions&quicksearch=sandbox