Each time I update Firefox it works fine but refuses to quit properly at the end of the session. I am using an iMac with OSX 10.11.3 which reports 'application unresponsive' after the attempted quit. However, 'Force Quit' is not successful either. I have to manually press and hold the power button to force a shut down. Once I restart, Firefox behaves fine until the next time an upgrade is needed. Have tried refresh and reinstall, but the same behaviour persists. Is there a fix or should I switch to another browser? Please help!