I noticed they weren't working either. Unfortunately I have no technical knowledge of this site,but I can assure you that it's not just a problem on your end.
I think if the gif is too large FA's software tries to make it smaller which takes away the animation. I don't know what "too large" would be specifically.
Yeah I feel you. Usually people will upload the gif with the additional link to the full resolution file in the description. Here's an example of one that I know works here though. Note that the file size is under 1 MB and the resolution is pretty low, something like 250x250
https://www.furaffinity.net/view/51155621/