[Pharo-users] making .extension files (like .class files)

hi everyone. I am facing a problem. I cloned a repo. of package. After that i tried saving and opening that package using Monticello Browser. But whenever i try save & open that package in pharo, all class and extension files are getting deleted and pharo is showing nothing in that package. Any suggestion??? One more thing i want to ask, i.e, how to make .extension files (like .class files) in pharo. Any resources on this topic? Thanks Rohit