I saw a similar thread to this from 2015, but the difference here, is that it will start working if I end the task. So here's the deal, I have a windows 7 desktop, a windows 10 desktop, and a windows 10 laptop, and all 3 have this very strange problem, and all but one of the devices are running crisp, clean, unaltered, default, stock as a block firefox. No add ons or anything fancy. What will happen (usually on a fresh start up of the computer it seems, but will do it other times too) is I will click firefox (either on the desktop, or the locked taskbar icon) and nothing happens. Because I already know whats going on, I open task manager, and there will be 2 or 3 firefox tasks running (even if I only launch it once) . If I end all these tasks and launch firefox again, it will work, and keep working. But every system I have has the same issue. Doesn't start the first time, and wont open the actual window unless you end the tasks and try again. I don't do custom install paths, I keep everything default. Firefox is usually the first thing I download and install onto a computer, so it shouldn't be any other programs messing with it. Anyways, really bizarre problem that has apparently been around for a few years.