Firenvim
A browser extension that turns any textarea into a Neovim instance, so text entered on a web page is edited with real Neovim inside Firefox, Chrome, or other Chromium browsers.
Firenvim turns a browser into a Neovim client. Clicking any textarea replaces it with an instance of Firenvim; writing with a save command sets the hidden textarea's content to the Neovim buffer's content, and a quit command closes the overlay and returns to the textarea.
It is specifically supported on Firefox and Chrome, with other Chromium-based browsers such as Brave, Vivaldi, Opera, and Arc expected to work without being specifically tested. It installs as a regular Neovim plugin through a manager such as lazy, vim-plug, minpac, or Vundle, followed by running its post-install script, and its behavior, including which sites take over textareas versus only offering a toggle, is controlled through a settings table in the user's Neovim configuration.