add: var pref = Components.classes["@mozilla.org/preferences-service;1"] .getService(Components.interfaces.nsIPrefBranch); 
context: function prefCacheSelectFolder(){  var fp = Components.classes[FILEPICKER_CONTRACTID]                     .createInstance(nsIFilePicker);  var prefutilitiesBundle = document.getElementById("bundle_prefutilities");  var title = prefutilitiesBundle.getString("cachefolder");  fp.init(window, title, nsIFilePicker.modeGetFolder);  fp.appendFilters(nsIFilePicker.filterAll);  var ret = fp.show();  if (ret == nsIFilePicker.returnOK) {    var folderField = document.getElementById("browserCacheDirectory");    folderField.value = fp.file.unicodePath;  }}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/49c400a322c8d0301f819861a70ad2869361a62f/pref-cache.js/clean/suite/common/pref/pref-cache.js