Você pode alterar a prioridade com:
sudo update-alternatives --install /usr/bin/x-www-browser x-www-browser google-chrome-stable <priority_as_integer>
Exemplo:
antes
$ sudo update-alternatives --config x-www-browser
There are 2 choices for the alternative x-www-browser (providing /usr/bin/x-www-browser).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/google-chrome-beta 150 auto mode
1 /usr/bin/firefox 150 manual mode
2 /usr/bin/google-chrome-beta 150 manual mode
depois:
$ sudo update-alternatives --install /usr/bin/x-www-browser x-www-browser /usr/bin/google-chrome-beta 50
update-alternatives: using /usr/bin/firefox to provide /usr/bin/x-www-browser (x-www-browser) in auto mode
$ sudo update-alternatives --config x-www-browser
There are 2 choices for the alternative x-www-browser (providing /usr/bin/x-www-browser).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/firefox 150 auto mode
1 /usr/bin/firefox 150 manual mode
2 /usr/bin/google-chrome-beta 50 manual mode