[Springtime]

Seems like a decent project, which has come up before. The sibling commenter ramraj07 would likely be interested in what seems like a new feature listed to automatically save pages once loaded, which according to that link works on Firefox for Android (mobile).

Back when Firefox supported the UnMHT addon it would also work on Firefox for Android and had the nice feature of being able to customize which replacement Unicode was used for illegal filename characters (instead of just using underscores like Chromium does and SingleFile says it does).

Btw the comparison table of SingleFile mentions MHTML can't be 'unzipped' to extract the resources but there is an open source program on Windows which can extract the resources called ExtractMHT[1], which later became bundled with Universal Extractor.

[1] https://www.legroom.net/software/extractmht