Rated 4 out of 5 stars

Developers: unMHT (very popular indeed) needs to be disabled (or uninstalled) before using this extension. Or else you get blank pages.
I had tons of old maff files that needed to be unzipped and reconverted to mht using unMht or Iexplorer. Pain in the Culo! but gladly kept old maffs until this extension came back to life!
Great stuff.

This review is for a previous version of the add-on (0.13.4). 

I and Arai worked together to make UnMHT and MAFF compatible, however it's still necessary to press a special button in UnMHT's preferences if you previously installed MAF version 0.7 or earlier.

I can confirm that, after this step, the latest stable versions of the two extensions do not conflict with each other in my system.