Review for Mozilla Archive Format, with MHT and Faithful Save by Lincky
Rated 5 out of 5 stars
It's really a regret of the discontinued support in the latest Firefox,
Alternative workaround,
1. Install Total Command (TC)
2. Download MAFF plug-in (decMaffWLX 2015.03.21) at https://totalcmd.net/directory/lister.html
3. Open TC and browse the zip file, double click, and prompt to install
Note, you can' directly open maff file by TC, the steps is to locate the maff file and click F3 or View to load the UI.
To create your own collections, you must have a Mozilla Add-ons account.