Vimium. Vim-like shortcuts for the browser. I can't name any other tool or extension that gives me anywhere near the productivity boost of Vimium. I spend probably half of my work day plus a few hours a day in my spare time in the browser, and it makes navigating the browser feel like butter. When I'm tired and don't want to be glued to my desk, I can relax and surf with one hand which just feels incredible. I quickly got so used to it that I instinctively try to use Vimium shortcuts when I'm on other computes and feel withdrawal symptoms if I realize that it isn't installed.
There also is quite browser, which is similar (not an extension though) it has some very cool features like domain conditional proxies and other settings
Surfingkeys is more customizable and has more features. You can use Surfingkeys API with javascript to add more customizations. It's good for adding custom keybindings to certain websites. Look at this config repo to see what's possible with Surfingkeys: https://github.com/b0o/surfingkeys-conf
It also supports neovim editing in browser, markdown previewer, pdf previewer with key bindings, etc.
Vimium is more robust as they have resisted the temptation to open their apis and allow unlimited customization. It's good for you if you don't have the need to add more customization or if you don't know programming.
Surfingkeys require you to know javascript a bit add advanced customization. And, it requires some troubleshooting when your config goes wrong. It's like Vimium for power users.
