Hey Yasl, sorry to bug you again so soon, but myself and a few others have noticed something a bit off about the avatars. You can't upload a gif to be an avatar. Like, if you have the gif saved on your device and try to upload it, it won't work. You have to upload the gif to an image uploading site (like imgur) and then use the "link avatar" function to actually make the gif work. Is that a bug or something? Is it possible to be able to upload gif avatars, or can the site not support that?
Ah, okay, that's apparently intended behavior. Specifically, it's meant to be a security feature. The forum re-encodes uploaded avatars by default but, due to a limitation in either the image library or the forum's use of it, doing so drops all but the first frame of animated GIFs (they're all munged into PNGs).
I expect the feature is designed primarily to prevent a scenario whereby a piece of Javascript (or perhaps some malicious executable) is uploaded and later executed in the context of the site, since the browser can't distinguish it from any other asset the site may serve. This could let the malicious actor steal session cookies (& thus your account) or what-have-you.
The safest way to solve this problem is to place all user-uploaded content on its own domain, hence you get "googleusercontent.com" and "derpicdn.net". The alternative is to make sure to only serve the images with an image-y MIME type, so the browser doesn't treat them as anything else. Alas, there is a long history of browser bugs and quirks that make this method exploitable, and it tends to be more fragile.
However, since uploaded avatars and attachments are not directly accessible as files on the website, but served up through the forum software, I'm going to assume (1) the forum software is sensible and only serves avatars with image-y MIME types, (2) browsers have sorted out the majority of such bugs, and (3) attachments could probably be exploited the same way and yet aren't re-encoded. And as such I've turned the re-encoding feature off.
Uh, let me know if it still doesn't work...
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