I'm not too hot with Linux, but what I gather he did was:

  1. Opened the Components folder in where he had downloaded (not compiled/installed) Firefox.
  2. Copied the file nsExtensionManager.js
  3. Then pasted the file to the Components folder in where he had actually installed Firefox.


I don't know where Ubuntu keeps its uninstalled copy of Firefox, so you might have to download Firefox again to get the nsExtensionManager.js file.