Actually, the releases page on GitHub does provide an .xpi file for Firefox, and it seems to be working fine. I guess the missing link on the website/README is a mistake.
Re:Wasavi – VI editor for any webpage
by mihaigalos on Monday January 16, 2023 @04:06PM
(#34405472)
I can confirm this. However, I constantly get a "View saved logins" to the top of the input field after I start typing.
Did you experience the same? I'm on Firefox 108.0.2.
Firenvim works in both Chrome and Firefox and you can harness the power of neovim, so that's a plus. Typing this from a neovim instance in firefox