Browsers are not supposed to be only "html document viewers". In spec parlance, they are supposed to be agents for doing whatever the user wants to do: that's why they also offer facilities for passwords, for example.
The fediverse is a bunch of web servers each with the accounts on it. When I am subscribed on instance A and go on an account on instance B, today the browser acts as a document viewer: I can see what the profile wants to show me, hopefully it has a button that properly redirects me but then I leave the context of the message I was looking at.
What I want instead is for the browser itself to offer me fediverse actions: like, comment, reply, directly from where the content I'm interacting with is. I don't expect browsers to do that soon so the next best thing is web extensions
In the host I had to change the owner to 1000. It was set to root somehow.