Firefox has its own Debian APT repo
Firefox has its own Debian APT repo
support.mozilla.org
Install Firefox on Linux | Firefox Help
Firefox has its own Debian APT repo
Install Firefox on Linux | Firefox Help
It does not seem to support alternatives.
I had to run
update-alternatives --install /usr/bin/x-www-browser x-www-browser /usr/bin/firefox 99 update-alternatives --set x-www-browser /usr/bin/firefox` xdg-settings set default-web-browser firefox.desktop