These properties are associated with the proprietary Mozilla xpconnect ("cross-platform" connect) services. These services allow scripts that have the correct security clearance to work with XPCOM (decidedly not MS COM) objects to extend the functionality of the application that uses the Mozilla engine (such as the Netscape 6 browser). Access to these services requires enabling security privileges (typically via signed scripts), as follows:

netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
// your xpconnect access code here
netscape.security.PrivilegeManager.revertPrivilege("UniversalXPConnect");