Generally after 2 to 5 hours of use, Firefox cannot connect to the internet anymore (and loses active connections such as from the Facebook Messenger page). When trying to close it, one process of firefox.exe will always stay active and also cannot be killed by the Windows Task Manager. Also restarting the program does not work, since it cannot start due to another instance already running. By then the only solution is rebooting the computer. This is going on now for about a week. I have had Firefox running on this laptop (Dell Precision M2800, Windows 7 Ultimate) as my major browser without major problems for years and have not recently installed any new software, but this is now becoming unworkable. The only things that have been the same for all times that it happened is that I had more than one window open with multiple tabs in at least one of the 2 windows and the www.facebook.com/messages page was open in the multiple tabs screen (since it is the tab that always stays open for me). Also the process of all the running firefox.exe instances that cannot be ended via any way, always uses around 300MB (±50MB) of memory. What I have tried so far: -Rolling back to version 66.0.4 (hoping it was a version related problem). -Full scan of my computer for viruses and malware. -Removing the original profile. -Uninstalling Firefox, including manually removing the Firefox related folders in AppData and Program Files and re-installing the latest version. Not installing any plug-ins or importing any of the previous settings or data. Edit: Running it in safe mode, gives the same result.