Hello, I have the same issue that Ferento posted about here 11 months ago: https://support.mozilla.org/en-US/questions/1355904 When starting a new firefox instance, it starts the window with the same size and position as the last instance had. However, when the last size stretched from top of the screen to the bottom, a new instance will always appear slightly shorter than the height of the screen, leaving a small gap between the bottom of the browser window and the bottom of the screen. The remembered size works perfectly for sizes less than the height of the screen. The xulstore.json file is not corrupt, as I've tried removing it and altering it, resulting in the same issue. I have also tried changing the window height inside the xulstore.json file to larger than the screen size, and found that it get's cropped to slightly less than the window height, same as my issue above. This has led me to believe that when firefox starts a new instance, the size is cropped so that it doesn't extend past the screen borders. This is good, but the size it gets cropped to is clearly bugged, unless it's intended to crop to less than screen size. I use a window manager that lets me easily snap windows to each other as well as to the screen borders, so firefox always leaving a slight gap when it starts drives me mad as I have to manually resize it every time. I use windows 10, firefox 106.0 (64 bit), however I experience the same issue with both firefox developer edition and firefox nightly.