Hello Marye815, Welcome to Mozilla Support! There are a couple of things you can try to fix this follow the steps, if one works, then you are done :) #1 Try to double-click/ctr-click the firefox icon and select "Quit". #2 Try to press the force-quit shortcut cmd+q #3 Use activity monitor (cmd+space -> "activity monitor" -> enter) From here, locate Firefox and click the "X" in the to left corner. #4 Open Terminal (cmd+space -> "terminal" -> enter) From here search for the Firefox Appliation using "ps -ef | grep firefox". Now you are presented with hopefully just one or two items named firefox. They have a 4 digit Pid Number. Then write "kill -9 Pid" (where pid is the number from the application). edit: to simplify the quit through terminal process, you can simply write "kill -9 $(ps -x | grep firefox) ". I hope this helps. -- Jørgen Juel