Depending on what you want to do, the annotation editor integrated in SingleFileZ might be sufficient. Otherwise, you have to run a HTTP server, unzip the file in a folder exposed by the HTTP server, and save the page you have modified via http://localhost with SingleFileZ.

EDIT: For practical reasons, this is not the best place to discuss about issues/feature requests. Please send me an email (cf. "Support email" here https://addons.mozilla.org/en-US/firefox/addon/singlefilez/) or create an issue here: https://github.com/gildas-lormeau/SingleFileZ/issues.