Avoid permission "Access your data for all websites" if possible

As of review https://addons.mozilla.org/en-US/firefox/addon/css-reloader/reviews/1774328/:

> This app asks for a full acces to all your web datas (including saved logins and passwords !) why ? I don't think an app needs such a a critical acces to remove some cache (another authorisation exists for that in firefox).
That makes me very suspicious, and I didn't install this add-on.

Start by reviewing the extension's declared permissions and the Firefox review linked in the issue. Determine whether CSS reloading can work without requesting access to all websites, then verify that the add-on still reloads site CSS while no longer requesting that broad permission.

Written by the indexing model from the issue text.