1. Open some pages
2. Scrolling with the mouse with the middle button or by clicking Up or Down in the scroll bar at the right of each page produces random black squares and rectangles that appear and disappear and some of them remains visible. Please look these images:
https://drive.google.com/drive/folders/ ... sp=sharing
The issue is not always reproducible. It happened for http://as.com just once. It hadn't happened for cyclingnews again, but it keeps happening for several pages from http://revistamundociclistico.com, e.g. http://revistamundociclistico.com/ruta/ ... lasov.html (pages with Disqus comments)
But it only happens in one of my computers, not in other computers

Thank you