Firefox - boxes and lines disapearing and not drawing properly

Since the upgrade? a little while ago (11 June 2020), with Firefox, 77.0.1 the boxes and lines that I draw on the screen, appear and disappear randomly when moving around the screen. This did not happen before. The box’s will draw 3 sides and leave the next blank. Horizontal lines disappear and reappear rather randomly, when scrolling around the screen. Is this a problem for other people as well?