FF won't open maximized on mon2 when mon1 is fullscreen

Using Win10 1903 18362.295 and FF 68.0.2

I have two taskbar menu shortcuts, one opens FF maximized on monitor1, the other opens FF maximized on monitor2. They work correctly.

BUT, when I am watching a video on monitor1 in FF fullscreen mode and then I click the shortcut to open a second instance of FF maximized on monitor2, that second instance always opens non-maximized. Its as though FF realizes that it has an instance open in full screen mode and that's why it opens the next instance in non-maximized mode, which perhaps makes sense for single monitor systems. I am hoping someone can tell me how to have the second instance override this behavior so it will open maximized on monitor2 like it always does. Thanks.