Hi,
About removing permissions to applications, see: https://discourse.flathub.org/t/flatpak-permissions-gui/40
bu it can also be done via command line: https://docs.flatpak.org/en/latest/flatpak-command-reference.html (search here for “permission”)
For a Firefox flatpak there’s this thread: https://discourse.flathub.org/t/firefox-flatpak-request/38
and Mozilla is working on it, see for example bugzilla bugs 1441922 and 1591387.
Request thread for Chromium: https://discourse.flathub.org/t/chromium-flatpak-request/87
No idea about the other browsers or qelectrotech.