fdo#72340 replace Netscape by Firefox in HTML compatibility options

Change-Id: Id17fe4a769f03722428b7d070c93c9a12e6ce215
Reviewed-on: https://gerrit.libreoffice.org/6969
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>