fdo#68546 Make menubar's text color of persona the same as Firefox

Change-Id: Ib9370f4b369f2baf29d118a1bbcd565bca005c30
Reviewed-on: https://gerrit.libreoffice.org/8712
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>