xdg-settings

Manage settings of XDG-compatible desktop environments. More information: https://portland.freedesktop.org/doc/xdg-settings.html.

xdg-settings get default-web-browser

xdg-settings set default-web-browser firefox.desktop

xdg-settings set default-url-scheme-handler mailto evolution.desktop

xdg-settings set pdf-viewer.desktop

xdg-settings --help