Stop Firefox from opening at restart
Every time I restart macOS (v10.12.4) on Mac Mini Firefox opens. I don't even use Firefox routinely, however, occasionally I need it when old fashioned website doesn't work with Safari — boy, is it slow by comparison! I looked and relooked at preferences to see where to shut it off to no avail. What might I do to get it to stop. Thanks.
Mac mini, macOS Sierra (10.12.4)