Screenshot - Responsive Design mode
How to recreate this issue:
1. Switch to Responsive Design mode, choose any device
2. Take screenshots made by manually "selecting elements on screen" or by" dragging area with cursor",
3. Copy and paste the image
4. The result shows the selected image with strange extended black background (both in width and height)
My FF version: 91.2.0esr (32-bit) I've been using FF's screenshot feature for a few years and never had any issues up until recent updates. (Screenshot under Desktop view seems to function normal so far as I can tell)