I guess there is no way to stop the gif data being loaded. Or maybe nobody is reading these posts. ;-(

If there is anyone interested in writing an addon to stop this, I would give a donation. ;-)

Some websites have animated images that aren't GIF images, but that are really short MP4 files and not GIF files that are covered by the image.animation_mode pref. You can possibly check this in the Inspector via the right-click context menu (Inspect Element).

• https://en.wikipedia.org/wiki/Video_alternative_to_GIF

You can block files with the gif extension in most adblockers, e.g. with uBlock.

Animated GIF images are hardly used these days, so do not get confused to think that this is about GIF images, so there are a lot more ways to animate content.

You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected to see what content this is about.

• https://developer.mozilla.org/en-US/Tools/Page_Inspector/How_to/Examine_and_edit_HTML
• https://developer.mozilla.org/en-US/Tools/Network_Monitor

Animated GIF images are hardly used these days

Not my experience, that is why I am asking how to block them from loading.

do not get confused to think that this is about GIF images

I'm not confused. My question is about animated gifs, not mp4s.

Incidentally I found an addon that does the trick. It's called Gif Blocker. https://add0n.com/gif-blocker.html

It prevents Firefox from loading the gif data completely, not just preventing it from being displayed