It is possible that your firewall or other security software 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 install 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 *https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating ---- Try to start Firefox in <u>[[Safe Mode|Safe Mode]]</u> by holding down the Shift (Mac: Options) key to see if that helps. If you have submitted crash reports then please post the IDs of one or more recent crash reports that start with "bp-": *bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx You can find the report ID of recent crash reports on the "Help > Troubleshooting Information" page (about:support). *click the "All Crash Reports" button on this page to open the <b>about:crashes</b> page and see all crash reports. Alternatively you can open about:crashes via the location/address bar. See also: *http://kb.mozillazine.org/Mozilla_Crash_Reporter *https://support.mozilla.org/kb/Mozilla+Crash+Reporter If you can't open Firefox, see: *http://kb.mozillazine.org/Mozilla_Crash_Reporter#Location_of_crash_reports *http://kb.mozillazine.org/Mozilla_Crash_Reporter#Viewing_crash_reports *https://developer.mozilla.org/How_to_get_a_stacktrace_for_a_bug_report