If you’re into programs with Vim-like key bindings, I can wholeheartedly recommend Qutebrowser. Back when Firefox transitioned from the old extension system and Vimperator stopped working, I started using Qutebrowser instead. I stopped due to the lack of good ad blocking, but sorely miss the key bindings every day. Will give it a new try now!
I use qutebrowser and Firefox + Vimium (as a lightweight layer of vim functionalities on top of Firefow). You may look a it but a little bit of configuration is needed to homogenize the keybindings between qutebrowser and Vimium.
I owe this a try as well. For me, vimperator/pentadactyl was an absolute dream. I kept them running for a long time, but eventually had to abandon them along with the old firefox versions. The WebExtension imitations don't even come close.
