Hey sometimes i have this problem and sometimes i dont.
I download an extension, (one that i just tried was the animPicture.mfx) I put the runtime one in runtime and the extension one in extension. And load up MMF2 as normal and its not displayed in the objects window. And if i try and load it from an external file MMF just crashes.
Ive tried it with the demo version, and the normal build. Is there somthing im missing?