Firefox doesn't close properly in about 50 % of cases. When closing FF, the window closes but the process firefox.exe isn't terminated. When trying to open FF again you got the error message "Firefox is already running, but not responding. To open a new window, you must first close the existing Firefox process, or restart your system." After terminating the process firefox.exe in the windows task manager, FF can be started again. Error only occurs when under "Options/Privacy/Use custom settings for history" at "Clear History when Firefox closes" the option "Browsing and Download History" is selected. All other options selected or not don't cause the issue. I switched this option it several times. When "Browsing and Download History" at "Clear History when Firefox closes" isn't selected, the error doesn't appear. Reproducible regardless if "Remember my browsing history" and "Remember download history" are selected or not. Reproducible: - after new installation of Firefox (Firefox 29.0.1 german, Windows7 64-bit) - with different profiles, even with all addons disabled or running in safe mode - with new profile with no addons or dictionaries installed - with windows firewall turned off and deactivated antivirus program - with hardware accellaration on and off I know the issue has already reported at bugzilla.mozilla.org and described at https://support.mozilla.org/en-US/questions/997918 https://support.mozilla.org/de/questions/997670 I want to describe the problem more precisely: It only occurs when "Browsing and Download History" is delete on exit. The other option at "Clear History when Firefox closes" don't cause this issue. Is there any other solution then to turn "Browsing and Download History" off?