Backport 1353013 - create preloaded newtab browser from an idle task, only in top window(s). (#4861)
Backport 1353013 - create preloaded newtab browser from an idle task, only in top window(s). (#4861)


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