// ARCHIVE HEADER
  1 - Version Major? (2)
  1 - Version Minor? (1)
  3 - Header (fmf)
  4 - Unknown (814)
  4 - Directory Offset [+9]
  4 - Header Size? (9)
  1 - null
  
// FILE DATA
  // for each file
    X - File Data
    
// DIRECTORY
  1 - Version Major? (2)
  1 - Version Minor? (1)
  3 - Header (fmf)
  4 - Unknown (814)
  X - Compressed Directory (ZLib Compression)
  
  when decompressed {
    // for each sub-directory
      4 - Directory Name Length [*2 for unicode] (not including the null terminator bytes)
      X - Directory Name (unicode)
      2 - null Directory Name Terminator (this field doesn't exist if the directory name length is null - ie for the root directory)
      2 - Number of Files in this Directory
      
      // for each file in this directory
        4 - Filename Length [*2 for unicode] (not including the null terminator bytes)
        X - Filename (without extension) (unicode)
        2 - null Filename Terminator
        4 - File Extension Length [*2 for unicode] (not including the null terminator bytes)
        X - File Extension (including the .) (unicode)
        2 - null File Extension Terminator
        4 - File Offset (relative to the start of the FILE DATA)
        4 - File Length
        4 - File Length
        
      2 - Number of Sub-Directories in this Directory
      // for each nested sub-folder
        // repeat from // for each sub-directory
    }

Uses ZLib compression for the DIRECTORY, doesn't appear to use any compression for the file data though