I have my Firefox (Developer Edition 71.0b4) shortcut setup to display the "Choose User Profile" window when I start it. (Since I maintain both a personal and work profile.) Lately whenever I start this window comes up completely blank, with no content inside it at all, although the Choose User Profile title is still present. This prevents me from selecting a profile and starting Firefox. To get around the problem, I close that blank window, wait a bit, and try launching the shortcut again. Often I have to try 3-4 times before it works. This problem had existed on a previous version of Firefox (sorry didn't note version then), but seemed to get fixed with an update several months ago. Now the problem has returned. I will try to attach an image later, but can't do so now while Firefox is running.