Very recently I started noticing something weird every time I launched Firefox. Whether it’s a normal session or private session it always happens. When I launch the application there is a small pop-up window that appears with squares of colors, like primary colors, blue, red, yellow. It appears for a fraction of a second. Has anyone else noticed this?
I’d guess it’s one of your extensions. Try disable all of them and see if it still happens.
Additionally, OP could probably stand to (re)run Malwarebytes.