For full flash animations as opposed to just gifs, (which i believe can be uploaded the same way regular images can) the protocol seems to be upload the animation to YouTube or another such video hosting site, then embed that.
Someone correct me if I'm wrong.
One last final hurrah, like the final defiant scream of a dying man.
Flash cannot be directly embedded because, aside from already being outdated and vulnerable, doing so would open up the website to incredibly dangerous and malicious abuse. Things that autoplay with speaker-breakingly loud audio, spam, spyware/malware, keyloggers, etc.
So once you upload your gif to Imgur or whatever, you right-click on the image and select "Copy image address". It should look something like this:
There should definitely be a ".gif" extension at the end of the link.
Now you go to MSPFA, log into your account, go to "Edit adventures", select your adventure, go to "Edit pages", type in your command (or not, I don't care), and in the box below where it says "Image", paste your image link. Then you click on the "Add page!" button and voila, you get something like this