Finally decided to tackle my maff/mht problem. Very impressed by this extension. After some quick testing, it does indeed open the resulting HTML in any browser cleanly and without issue (tested with FF, Dillo, Links2, Pale Moon).

fyi: if you're like me and have saved many web resources as mht/maff files over the years (and likely scattered throughout many subDirectories, on external storage), Pale Moon can still handle those those two via extension (if finding and re-converting to WE is a major project).