Gnome Web is based on WebKit.

I should have added “cross-platform”. It’s not a viable alternative for most Firefox users.

There are several, just none that are still maintained. But webkit is still open source and there's no reason someone could not fork or start up a new browser project with 90% of the work already done by webkit, you just need a GUI.

Emacs supports browsing with WebKit: https://www.gnu.org/software/emacs/manual/html_node/emacs/Em...

This is distinct from its own Emacs Web Wowser, which is a more primitive browser (but quite good for quite a lot!).

> There is no open-source browser based on it that you could use as an alternative to Firefox.

here you go:

https://github.com/duckduckgo/apple-browsers