Mozilla is still doing something with the keyboard shortcuts API to make that more capable. I don't know what exactly they're doing, it won't be as powerful as Vimperator, but it should be a good bit more powerful than Vimium.

This (obviously) won't be in Firefox 57, but should be ready relatively soonish after. So, this is something that they have already been actively working on for a few months. I'm guessing 59 or 60 from how I've heard it described.

Yes, Mozilla + volunteer contributors. Check the last comments in this: https://bugzilla.mozilla.org/show_bug.cgi?id=1215061

There was a meeting today and the contributors participated in it.

I’m sad that I’ll have to stop using VimFX, it was the best Vim plugin I could find. It was lightweight and did just what it had to (I absolutely hate the custom search/address bar thing in Vimium). My alternative right now is Saka Key. I hate the default keybindings, but you can customize them all you want. The thing I miss the most right now is being able to focus on the address bar (pressing “o” with VimFX). I’m not sure if it’s possible with the current WebExtensions API.

Yes, but in VimFx's case it's more a matter of the developer not feeling like it considering Vimium is available, which for me has been a drop-in replacement of VimFx. I just assumed that as you mentioned Vimperator, you wanted the complete, somewhat more invasive, experience.

Note: I should correct this. It's not about the developer not feeling like it, but about him only wanting to do it without having to work around API limitations like Vimium had to: https://bugzilla.mozilla.org/show_bug.cgi?id=1215061#c3

It's preferable, but if I'm honest Vimium is Good Enough(tm) for my general use case. I didn't realize they had a FF57 compatible version :)

Vimium is /mostly/ there, but gaps in the WebExtensions API make the experience rough in my experience.

The biggest issue for me, right now, is that there are a lot of places where FF won't allow WebExtensions to intercept key events for shortcuts, like on the new tab page, error pages, any other "system" pages, or certain pinned tabs (this one is particularly inconsistent). This means that if I'm jumping through several tabs with J/K and hit any of those by accident, I'm stuck there until I figure out what happened and either use the mouse or the official hotkeys to switch back out.

Same with focusing the URL bar and the slightly quirky experience of the omnibar that Vimium has to use instead.

It works, but mostly serves to remind me how much I miss VimFX rather than to improve my productivity.

I'm using vimium in nightly right now.