See
Visual Kindle Guide. The page on command prompt tells you how to open a command window and the page on KindlePID tells you how to install Python. Don't worry that you don't have a Kindle, since all Python scripts work similarly. The ereader2html.py script works similarly to KindleFIX, except that it needs more arguments. See
eReader Decoder Tool. Once you have the HTML (plus images) in "outdir" then Calibre can convert the HTML to LRF for you.