code: function softwareUpdate_forceFallback() {
      var dirService = Cc["@mozilla.org/file/directory_service;1"].
                       getService(Ci.nsIProperties);
  
      var updateDir;
      var updateStatus;
  
      // Check the global update folder first
      try {
        updateDir = dirService.get("UpdRootD", Ci.nsIFile);
        updateDir.append("updates");
        updateDir.append("0");
  
        updateStatus = updateDir.clone();
        updateStatus.append("update.status");
      } catch (ex) {
      }
  
      if (updateStatus == undefined || !updateStatus.exists()) {
        updateDir = dirService.get("XCurProcD", Ci.nsIFile);
        updateDir.append("updates");
        updateDir.append("0");
  
        updateStatus = updateDir.clone();
        updateStatus.append("update.status");
      }
  
      var foStream = Cc["@mozilla.org/network/file-output-stream;1"].
                     createInstance(Ci.nsIFileOutputStream);
      var status = "failed: 6\n";
      foStream.init(updateStatus, 0x02 | 0x08 | 0x20, -1, 0);
      foStream.write(status, status.length);
      foStream.close();
    }
docs: Update the update.status file and set the status to 'failed:6'