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Vimium-FF works pretty well for me.

Try Tridactyl,

https://addons.mozilla.org/en-US/firefox/addon/tridactyl-vim...

No, it's impossible for the moment to deliver reliable keybinding-extensions. Firefox has no API for it, so all solutions need to work by injecting a script into each website, and grap keys from this context. And that simply sucks and leads to many problems. They are supposed to work on a solutions, but it likely still needs 6+ months.

Besides that, vimium works well enough under perfect conditions, and is quite mature as it is a port from Chrome. Tridactyl is also promising replacement for Vimperator, but still needs time to grow, because they just started some weeks ago.