The Tor Browser / file revision

 function getCacheService()

 {

     var nsCacheService = Components.classes["@mozilla.org/network/cache-service;1"];

     var service = nsCacheService.getService(Components.interfaces.nsICacheService);

     return service;

 }

 function createCacheSession(clientID, storagePolicy, streamable)

 {

     var service = getCacheService();

     var nsICache = Components.interfaces.nsICache;

     var session = service.createSession(clientID, storagePolicy, streamable);

     return session;

 }

 function openCacheEntry(clientID, url)

 {

     var nsICache = Components.interfaces.nsICache;

     var session = createCacheSession(clientID, nsICache.STORE_ANYWHERE, false);

     var entry = session.openCacheEntry(url, nsICache.ACCESS_READ_WRITE);

     return entry;

 }

 function wrapString(str)

 {

     var nsISupportsCString = Components.interfaces.nsISupportsCString;

     var factory = Components.classes["@mozilla.org/supports-cstring;1"];

     var wrapper = factory.createInstance(nsISupportsCString);

     wrapper.data = str;

     return wrapper;

 }

 function test()

 {

     var data = wrapString("javascript");

     var entry = openCacheEntry("javascript", "theme:button");

     entry.cacheElement = data;

     entry.markValid();

     entry.close();

     var newEntry = openCacheEntry("javascript", "theme:button");

     if (newEntry.cacheElement === data)

         print("object cache works.");

     else

         print("object cache failed.");

 }

 test();