Who develops vimperator these days? Some of their primary maintainers moved onto a separate project called Pentadactyl[0] a few years ago.
A much bigger problem is that Firefox is moving (has moved?) away from XUL and XPCOM, a move which permanently breaks extensions like Pentadactyl (and Vimperator too).
Already Pentadactyl is broken for me on the latest versions of Firefox and Pale Moon (though I can't say for sure that it's because of XPCOM and XUL or for some other reason).
In addition, the Pentadactyl nightly builds aren't signed, so if I want Firefox to allow them to be installed I have to run the Firefox Developer build and make a global preference change to allow all unsigned extensions to be installed.
This breaking of my favorite extensions on Firefox has made me move to Pale Moon, where Pentadactyl was working until recently. Now that Pentadcatyl doesn't even work on Pale Moon anymore, I'm not sure what to do.
It works for me on Firefox 50.1.0
But the move away from XUL is indeed worrisome for plugins like these... I kinda hope someone will just build it into the servo project and make that into a usable minimal browser.
I'm a little wary of installing addons from some random github repo.
FWIW, I use willsALMANJ's releases with no problems, he was/is quite active on the pentadactyl issue tracker.