They've got coverage of ~70% of WebExt and growing, including on iOS, which is awesome:

Since I know niche-browser support isn't a likely one, just know there's no hard feelings if this doesn't happen. 💜 (Although maybe very slight hard feelings that I can't publish a patch myself, since it's not open-source; and can't even easily fix it for myself since the source is minified. ;)

Cross-reference: listed on their tracker here: https://orionfeedback.org/d/10590-the-oauth-return-for-the-graze-for-mastodon-extension-fails