We are facing the Problem that Firefox won't start anymore as of the update to version 58.0 from 57.0.4 and less. This Problem bothers ca. 90% of our Clients. When you try to start the Firefox Application, Windows acts like trying to load but doesn't succeed and nothing happens ever after. When you take a look at the Task Manager, it has open one Firefox Process. A "closer look" to the Performance Monitor of Windows shows, that this Process hat 3 Threads started. but doesn't use any CPU or RAM. On a Client, where the update succeded, we have like 6 started Processes with round about 150-200 Threads. If we uninstall the Firefox and install the previous version 57.0.4, it works just fine, for as long as the update doesn't happen. Meanwhile we tried to delete everything of a faulty version that we could find, including reg keys, profiles etc. and do a clean install. We tried to start Profile Manager, Firefox in Safe Mode, but none of it worked. The only thing that worked, is to start the OS in Safe Mode and open Firefox. In there it worked just fine. We are using Windows 7 with the latest Service Packs and Hotfixes/Updates and the latest drivers possible.