Pentadactyl isn't the successor to Vimperator, it's just a similar extension with a different feature set and some former Vimperator developers working on it. From what I understand, Vimperator continued to be developed after Pentadactyl was born. Long ago I compared the two and decided to use Pentadactyl because it seemed to be more powerful, but I'm not sure how they compare these days.

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.