I discovered today that Firefox 57.0.4 no longer is able, even via add-ons, to display MHT files (confirmed Google Chrome doesn't either ... I don't know if it ever did). https://support.mozilla.org/en-US/questions/1192784?fpa=1 implies that this functionality degradation is/was by planned design.
Is there some software that can convert an existing .mht file, stored on disk, from that format to some other format that will load into all web browsers on both Linux and Windows systems without requiring browser extensions?
The file format needs to be a single file, not a link to a "index.html" file on disk that points to files living in subfolders. That is what I thought the "web archive" was supposed to provide.
The software that does the converting does not have to be platform-neutral, but it has to be zero cost (meaning download and run, not download+compile+run, not pay X USD + download + run). Ubuntu-specific and Windows-specific is ok.
However, the resulting file format should just render completely in the browser without requiring the user to download additional software.