Can't find any other files with FExplorer with .mbm extension. Somebody correct me if i'm wrong.
Every app. uses .mbm files to render their interfaces, I won't go throug examples because it would take too long. Just one, the arrows and the folder images in eFileManager are strored in a .mbm (they're like an animated GIF).
The bad thing is, .mbm files are very big. (In relation with a JPG)