Some few animated gifs or looping videos cause firefox to briefly become unresponsive and/or go white for a moment, after which most pictures (on all firefox tabs and windows) are no longer displayed. If the Shockwave Flash plugin is enabled and running something in another tab, that crashes too. Most videos seem fine, but when one causes the issue, it causes it consistently. The first "animated picture" (it's a video) on this page is an example I've been testing with: https://www.urbandictionary.com/define.php?term=Nya The issue happens when manually starting that video, or when scrolling down until the bottom of the firefox window reaches the bottom of its preview area (which I assume normally triggers it to play?). This only happens on Firefox. In Opera, it plays as soon as the page is open and scrolling past it causes no issue. Testing once with the Windows 10 Task Manager opened while triggering the issue, some error report briefly flashed at the top of the process list, and it seemed as if the whole Windows UI flashed as well (after that the screen had become brighter and more blue, which I first attributed to some reduced colors mode, but more likely was brightness being reset to a higher setting and perhaps a previously enabled "Night light" mode getting turned off at the same time). I first noticed the issue sometime last month in the week following both the Windows 10 mass forced upgrade to 1903 and a Firefox update (making it hard to tell if either caused it, and the grace period to roll back that Windows update is over anyway). Before that the issue never happened. NVidia graphics driver has already been updated. Already tested with all add-ons disabled, and with plugins disabled (including flash). The most effect that had was getting to scroll past the bottom of that video without it starting, but even that wasn't consistent, and in any case trying to start the video would still trigger the issue. This question is the closest report I have found since, however unlike that user I do not get the issue in other browsers: https://support.mozilla.org/en-US/questions/1264003 Like that user, the http://html5test.com/ page shows no on "MPEG-4 ASP support" and "H.265 support", and the Web Console shows nothing new when the issue happens.