Animated GIF images are slow on iOS
I visited the link provided, and I was unable to recreate this issue. The speed of the animations seems perfectly fine on iPhone 4S. If you have had this problem on numerous devices, I kindly suggested reporting it to Apple as a potential bug. More than likely, if it hasn't already been reported, an engineer will get back to you with a request and instructions on how to submit more information regarding the matter to them.

To submit a bug report to apple, visit http://bugreport.apple.com.

I would also like to suggest downloading Google Chrome for iOS or Opera Browser for iOS and visiting the same website(s). See if the animations are just as slow there. This will give you a bit more detail to submit to Apple with your bug report. If the issue is only in Mobile Safari, that will help them track the problem down much faster. If it exists in all browsers on the device, they will know that they need to look a bit deeper into iOS itself. Either way, I'm afraid I can't offer a quick fix for the issue as it seems to be a rather rare occurrence.

Good luck and happy LOLing!