Chrome Web Store warnings and Manifest v3

[zplan]

The extension is currently shown as not compatible with Manifest v3 and therefore deactivated soon.
Would it be possible to migrate the extension to make it Manifest v3 compatible?

[seansfkelley]

I'm open to it and would accept a PR, as long as it continues to be compatible with both Firefox and Chromium-based browsers (which might be a little annoying since one demands service workers and the other background pages, though maybe just specifying both will Just Work?). I'm unlikely to address this myself in the near future due to time contraints.

[seansfkelley]

As of just a couple weeks ago it looks like Firefox is implementing the combination of v2 and v3 features, so it seems like this extension should be able to switch to v3 and have everything just work in all browsers, since it doesn't use any v2-only features. That would still require a bit of a rewrite to service workers, but the extension already uses async communication protocols with the common background page so architecturally it should be pretty similar.

I still don't have enough time to dig into this myself, but would test/merge/release a PR that does it.