https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

You can check for problems caused by recent Flash updates and try these: *disable a possible RealPlayer Browser Record Plugin extension for Firefox and update the RealPlayer if installed *disable protected mode in Flash 11.3 and later *disable hardware acceleration in the Flash plugin *downgrade the Flash player to version 10.3 or 11.2 *http://kb.mozillazine.org/Flash#Troubleshooting *http://helpx.adobe.com/flash-player/kb/flash-player-113-crash-mozilla.html ----- A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program. Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process. See: *https://support.mozilla.org/kb/Server+not+found *https://support.mozilla.org/kb/Firewalls