So yeah, Imgur relies pretty heavily upon gifv and it would be great if Kirby supported the image format!
If you try and use it in your content now, you just get a broken link.
The easiest way around it is to remove the ‘v’ from the ‘gifv’ extension in the link but that’s not a very elegant fix.
There is a problem: imgur is just cheating when it is showing gifv. Gifv is just another name for some high-quality MP4 video.
So just enter gifv in a video tag and everything will be fine. 
In fact, they convert to webm and mp4, as they explain in their blog http://imgur.com/blog/2014/10/09/introducing-gifv/
The cornerstone of Project GIFV is a platform-wide upgrade to automatically convert uploaded GIF files on the fly into the WebM or MP4 video formats, depending on browser support.
And if you look at the source code of one of these URLs with the extension .gifv, you will find a video tag with both webm and mp4 videos embedded.