Vimium these days does not work when a page hasn't finished loading and it doesn't work on blank pages (about:blank) or any other "system page" (like the preferences or addons). The "o" key can no longer highlight the address bar but brings up a non-native address bar that does not find my bookmarks as it should.
Imagine you couldn't click on another tab with your mouse pointer while the current active one is loading. Yes, it's as terribly frustrating as it sounds.
In the XUL days I could even hit a key to make every button in Firefox UI accessible via keys. VimiumFX gave me the best browsing experience I've ever had and it's gone. WebExtensions Vimium is nothing buta painful reminder.
Qutebrowser may seem like an acceptable remedy, but giving up all the add-ons (mainly uBlock Origin and Tree Style Tab) makes it a no go.
As the_pwner224 points out, Vimium-FF is probably the way to go if you want to give this a try despite its shortcomings...