g_app_info_get_default_for_type() will fail on OpenBSD's veiled
filesystem since we most likely don't have direct access to the binaries
that are registered as defaults for this type. Fake it up by just
executing xdg-open via gio-launch-desktop (which we do have access to)
and letting it figure out which program to execute for this MIME type.
This has the side-effect of ignoring/losing MIME types associations
registered in firefox prefs only.
Differential Revision: https://phabricator.services.mozilla.com/D51388
--HG--
extra : moz-landing-system : lando