firefox automatically upgraded to latest version today but did not start. i checked the task manager and an instance of firefox was already running, but the browser screen is not seen. i ended the process and restarted firefox with the same result. i tried reinstalling firefox twice, once with earlier version and then with latest version, but no success. i use windows 7 updated, no firewall issues, no antivirus issues, no malware or virus. recently installed and uninstalled mac visual styles for windows, but firefox was working even after that installation