Hi, thanks for the review. This was a Firefox issue, cf. https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/. Unfortunately, there is nothing I can do personally to correct this problem. It should be fixed if you let Android updating your browser.

Edit: I published approximately 10 versions since your review. Are you still unable to install the extension?

Thank you for the review. I do my best to make the saved pages as small as possible by removing the most of unnecessary HTML and CSS. It is already a lot of work, unfortunately I can't do more.

Edit: actually I can do more, check SingleFileZ here: https://github.com/gildas-lormeau/SingleFileZ

Thank you! Now there's also SingleFileZ :)
More info here: https://addons.mozilla.org/firefox/addon/singlefilez