check:
gio open http:\\www.google.com
gio mime x-scheme-handler/http
gio mime x-scheme-handler/https
    https://github.com/telegramdesktop/tdesktop/issues/24506
    https://help.gnome.org/admin/system-admin-guide/stable/mime-types-application-user.html.en
xdg-mime query default x-scheme-handler/https

xdg-open https://google.com
xdg-settings get default-web-browser
xdg-settings get default-url-scheme-handler https
xdg-settings get default-url-scheme-handler http
xdg-settings set default-url-scheme-handler https

update-alternatives --display x-www-browser
sudo update-alternatives --config x-www-browser
    ls -l /etc/alternatives/x-www-browser
    ls -l /usr/bin/x-www-browser
sudo update-alternatives --install /usr/bin/x-www-browser x-www-browser /var/lib/flatpak/exports/bin/org.mozilla.firefox 210
sudo update-alternatives --remove x-www-browser /var/lib/flatpak/exports/bin/org.mozilla.firefox 210
    https://unix.stackexchange.com/questions/584478/how-to-add-browser-to-update-alternatives

update-alternatives --display gnome-www-browser
sudo update-alternatives --config gnome-www-browser
sudo update-alternatives --install /usr/bin/gnome-www-browser gnome-www-browser /var/lib/flatpak/exports/bin/org.mozilla.firefox 210
sudo update-alternatives --remove gnome-www-browser /var/lib/flatpak/exports/bin/org.mozilla.firefox 210

~/.config/mimeapps.list
[Default Applications]
text/html=org.mozilla.firefox.desktop
x-scheme-handler/http=org.mozilla.firefox.desktop
x-scheme-handler/https=org.mozilla.firefox.desktop
x-scheme-handler/about=org.mozilla.firefox.desktop
x-scheme-handler/unknown=org.mozilla.firefox.desktop


https://support.mozilla.org/en-US/kb/make-firefox-your-default-browser
https://support.mozilla.org/en-US/kb/setting-firefox-default-browser-does-not-work

https://osnote.com/ubuntu-default-browser/
        ??? no choice for firefox

about:policies
    DontCheckDefaultBrowser: true

flatpak firefox default browser
https://unix.stackexchange.com/questions/614899/setting-a-flatpak-app-as-the-default-web-browser
https://ubuntu-mate.community/t/setting-the-flatpak-firefox-app-as-the-default-web-browser/25895/2
2019
https://github.com/flatpak/flatpak/issues/3216
    gio mime x-scheme-handler/http firefox.desktop
    gio mime x-scheme-handler/https firefox.desktop