I observe the same behavior described and illustrated by Birdbrain. I'm using Firefox version 93 on Windows 10 computer. I think the odd behavior started with version 93 but not sure if Windows could have anything to do with it. Definitely didn't have the problem behavior until after that 93 update. All other applications outside the Firefox container/browser on this computer work fine with the drop-down objects they utilize. Within that Firefox print dialog open, scrolling down to the very bottom of the dialog, directly above the "save" and "cancel" buttons, there's the hyperlink to "Print using system dialog...". which opens a Windows print dialog and perhaps could be more or less useful as a workaround. Hopefully this reported problem will be prioritized soon by Mozilla development for improvements.