Once in awhile, my MacBook Pro seems to become "confused" b/c I've left too many apps open or too any word dox open, or a combination. It basically refuses to process. I shut if off [cold re-boot]. When I re-open the Firefox logo in the tool bar at the bottom is gone, replaced with a question mark [?]. Eventually, I find some way to reinstall the app; and everything resumes was normal. There must be someway to avoid this. What is it please? Btw, I'm older and not especially tech savvy so please try to keep any suggested steps to resolve this in very plain English.