dvipng -T tight -D 144 -bg Transparent Sounds good to me. I installed these changes (including the Windows path stuff) in TL just now.
Is there any hope of factoring out commonalities in the env files? For example, if some kind of tex4ht macro can expand inline, such that one source line could expand to i~/tex4ht.dir/texmf/tex4ht/ht-fonts/mozilla/! and i%%~/texmf-dist\tex4ht\ht-fonts\mozilla\! in the two respective output files, an enormous amount of duplication could be avoided. Also, regarding those "win32" lines, I doubt mixing / and \ paths is desirable. Maybe better to unify them all to / ...? I don't know, though. Thanks, Karl