Mine

C:\moz-debug\mozilla\ff\dist\bin>xpt_dump.exe C:\moz-debug\mozilla\ff\xpcom\io\_xpidlgen\nsIStringStream.xpt
Header:
   Major version:         1
   Minor version:         2
   Number of interfaces:  2
   Annotations:
      Annotation #0 is empty.

Interface Directory:
   - ::nsIStringInputStream (8f6053fc-0944-4270-89e1-12c3113d44e8):
      Parent: ::nsIInputStream
      Flags:
         Scriptable: TRUE
         Function: FALSE
      Methods:
   G     uint32 data(in dipper retval CString &);
    S    uint32 data(in CString &);
         uint32 setData(in string, in int32);
     H   uint32 adoptData(in void *, in int32);
     H   uint32 shareData(in string, in int32);
      Constants:
         No Constants
   - ::nsIInputStream (fa9c7f6c-61b3-11d4-9877-00c04fa0cf4a):
      [Unresolved]