Quite cool.

You could distribute it as `.html` only, and use JS to offer a local download link to itself in the correct extension. A polyglot installer, of sorts.

For example, this gist is an HTML that, when opened, offers a download zip of its DOM in whatever state it currently is:

https://gist.github.com/alganet/c904acb57282402fc0bd724f1eeb...

I think you can use something similar to get the entire page contents as a blob, but I never tested with binary data in actual browsers. Perhaps even patch it to avoid the initial windows error.