You asked in developer's forum and you were answered, but you stopped keeping an eye on the thread to follow your problem.
Thumbnails work fine, but the image must be in Introtext. In addition, as normal, MFPE works with the article's system of Joomla, which is used or loaded by majority of third extensions to write articles. If you don't use the Joomla system to submit articles, and the extension you have doesn't use the article's Joomla component, MFPE probably won't work. I can't do my extension compatible with all other over the world.