Latest update causes problems logging off. Want to uninstall but it will not. Requires reboot before uninstall even after rebooting.

The first time I updated Firefox it would not run. I have tried to avoid the updates but it keeps installing. Now my computer does not log off properly. Also, several times my Mcfee Internet Security has been shut-off. I have tried to uninstall Firefox but get the message"Firefox must be restarted to complete a previous upgrade of Firefox. Do you want to reboot now?" If you say yes and reboot, you get the same message again. It seems Firefox is stuck mid installation