The author mentions the loss of vim-like web browser controls when the Pentadactyl extension didn't convert over to the webextensions api.
You get the vim functionality back with the following extensions:
Firefox -- Vim Vixen (https://addons.mozilla.org/en-US/firefox/addon/vim-vixen/)
Chrome -- cVim (https://chrome.google.com/webstore/detail/cvim/ihlenndgcmojh...)
A bit tangential, but would you know if there is an extension that would provide Vim bindings only in textfields? I really miss not being able to use regular expressions (or simple search) in a plain text input.