chore(nobug): Do not build about:library in buildmc (#4527)
chore(nobug): Do not build about:library in buildmc (#4527)


sarracini/activity-stream,mozilla/activity-stream,rlr/activity-streams,rlr/activity-streams,mozilla/activity-streams,rlr/activity-streams,mozilla/activity-stream,mozilla/activity-stream,sarracini/activity-stream,Mardak/activity-stream,mozilla/activity-stream,rlr/activity-streams,Mardak/activity-stream,Mardak/activity-stream,Mardak/activity-stream,sarracini/activity-stream,mozilla/activity-streams,sarracini/activity-stream