I have the latest update. Gyfcat links do not embed on posts.
Using firefox : i can see the preview in the composer but not in the thread as even discourse is having similar issue from my side at-least.
used http://gfycat.com/FirsthandMeekAfricanaugurbuzzard
Sure @techapj can you have a look?
I also get the same bug on the latest google chrome.
I just looked into it, this issue is only occuring on SSL enabled instances because of a change introduced by Gfycat.
Gfycat is no longer serving iframe content (in oEmbed) over secure connection (HTTPS), hence SSL enabled Discourse instances are giving following error when trying to onebox Gfycat link:
Mixed Content: The page at 'https://meta.discourse.org/t/gyfcat-onebox-bug/35916/3' was loaded over HTTPS, but requested an insecure resource 'http://gfycat.com/ifr/FirsthandMeekAfricanaugurbuzzard'. This request has been blocked; the content must be served over HTTPS.
oEmbed URL: http://gfycat.com/cajax/oembed/FirsthandMeekAfricanaugurbuzzard
The proper fix for this is that Gfycat should be serving iframe over HTTPS. I will try to bring this issue in their notice.
The last option would be to create a custom Gfycat onebox, where I will have to force the Gfycat iframe URL to be served over HTTPS.
With the new update can we onebox gfycat now on HTTPS?
Reported this on Twitter:
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Will follow up 
Are there any updates on this. I did like the gfycat onebox with discourse
Does it work now? Can you try it?
Yes gfycat has been working good these past few months.