MAFF is a format used by firefox.I hope you have downloaded this addon which enables you to save as MAFF and MHT format.I had the same addon and had been using it for a long time.MAFF will just like take a screenshot of whole page and display you links and texts.But MHT is different,I tried the same as you told.Saved as mht format and when I view source(CRTL+U).It was perfectly fine.Just select webarchive,MHTML format and save.Then try viewing source code.Hope it will work fine,

A MAFF file is a ZIP archive, so you would have to extract the files in a archive manager if you do not use an extension to handle this kind of file.