The posted extension is about using vim key bindings to navigate links and other useful common commands. Firenvim is about embedding an nvim instance in an text input field. Apples and oranges.
I have been using tridactyl for the better part of this year. It is amazingly powerful, very fast for navegating with the keyboard. I miss the keybindings when I’m in other computers/browser
* https://github.com/qutebrowser/qutebrowser
* https://github.com/philc/vimium
And https://vim.reversed.top/ (list of Vim-like applications and plugins)
[0] https://github.com/glacambre/firenvim