I'm currently in the process of taking over as maintainer for the emacs-keybindings addon for Firefox.

I've just published the first update in years, with changes including:

• tested on Windows and Linux now
• some functionality is now configurable: debug logging, custom new tab page, experimental features, modifier-less high level bindings
• all keybindings are listed in the options settings page
• M- keybindings are now also reachable via ESC
• M-< and M-> was added for scrolling to top/bottom
• introducing prefix key, currently only used for opening/closing of windows (C-u C-x C-f or C-u C-k)
• search is introduced as experimental feature - currently it just highlights all matches
• the extension now registers as browser action in preparation for additional features

Unfortunately a lot of things that used to work with the old XUL plugins few years back just don't work with the new APIs - and Firefox developers have been sitting on relevant bugs for 8 years or more without anything happening now - so this is probably close to the best we can have for now. In combination with setting editing keybindings either via Gnome settings or AHK it makes browsing almost bearable again.