Two years without the APIs making a port possible.
So yeah, the Firefox devs didn't have much to go on except inactionable "just do whatever Vimperator needs" junk, and no other vested interest seems to have lifted a finger to help the VimFX guy speed up his work on the experiment after he finally got the ball rolling, so blame doesn't really rest on the Firefox devs here.
One of the lead Firefox extension API devs is also the primary Pentadactyl (and former Vimperator) dev. I'm sure they were aware of exactly what was needed for that and similar extensions. They also made it clear from their earliest announcements that they intended supporting these extensions.
It simply isn't a priority which may be fair enough.
Pentadactyl still works well on ESR.
Other addon devs did help push things along, and they got the abilities they needed much sooner. We can only excuse ourselves so far before we share in the responsibility for things not getting done.