I don't know about Ferro, but even vimium asks for this many permissions. I guess this due to the way it will handle shortcuts and bindings. I was hesitant to install vimium because of this but it is open source and the author seems to be someone famous so I can trust them. Related vimium ticket:
https://github.com/philc/vimium/issues/366
TL;DR: not very unexpected perhaps?