So I made a new file in Firegraft and edited a few things. Then I saved it as an .exe file, but when I click on the .exe file to start it up, it just opens a browser and asks me for another .exe to use. What am I doing wrong?
None.

Ultraviolet -- That's strange, it looks like you targeted the base image file (sometimes people make the mistake of just using the imgur page link which doesn't work for embedding) but it still didn't work it sounds like.
NudeRaider -- I think SEN has trouble with https or hotlinking is forbidden. It certainly is nothing about the size, it just fails to get any size. You can get it working if you use imgur and include the actual image link for the img tag. Like this: [img=https://i.imgur.com/ddYqXZa.jpeg]
Symmetry