I can't say fat morphs are common over here. That's more of DeviantArt's territory. There are apps you can use. I can't recommend any, but a quick google search will pull up a bunch. If you want to post your fat morph nudes on FF, just remember you can't show your genitals.

Darling, if you want decent, then you'll need to use something like photoshop.

That could be you if you learn how to use the program.