I've been using Vimium since I use firefox (for around 3 years).
It's annoying that Vimium can no longer control the browser UI and is limited on some pages (New Tab, mozilla.org) but this is necessary for security.
Why? You can't read the source of this addon and evaluate whether or not it should have this access? This should be a permission that you can grant to an addon, we're not children that must at every juncture be managed so they don't burn their fingers.
I actually use a vim-style plugin in Firefox and this seems obvious to me, how do you think the majority of users feel?