Can I trust the permissions section of an extension? If Firefox says an extension only has access to a single website, can I trust it or can an extension installed from the official website go rogue anytime and have access to any site I go to? I mainly use Firefox but I don't have the confidence to install so many add-ons because there's no indication that it's currently accessing the site or not. about:performance don't always tell the whole story and a working extension can not show itself there.

Other browsers can set which site has an extension can have access to. You also have a clear indication that it's currently ON by hovering at the extension icon where a "Has access to this site" message will appear. Hope we can have something like that in Firefox soon.