>I am troubleshooting the known "Firefox cannot open file dialogs" error, with Firefox printing this message on every attempt: Gtk-WARNING **: 22:45:36.767: Can't open portal file chooser: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface “org.freedesktop.portal.FileChooser” on object at path /org/freedesktop/portal/desktop
>The problem was in /usr/share/xdg-desktop-portal/portals/gtk.portal and the fact that the session was using i3wm. Changing UseIn=gnome to UseIn=gnome;i3 in that file resolved the problem.
>In general, $XDG_CURRENT_DESKTOP must be in the UseIn= stanza in the file. In my case it was i3.
xdg-desktop-portal-kde krashes, and xdg-desktop-portal-gtk wont load outside a GTK destkop, back to Gentoo for me.