Thank you! Fortunately, HTML is already a standard :). MHTML is almost dead, Google will probably withdraw its support on Chrome in favor of... Web Bundles (https://web.dev/web-bundles/). Mozilla said they do not want to implement this new specification in Firefox because of the potential security issues it would introduce, see https://docs.google.com/document/d/1ha00dSGKmjoEh2mRiG8FIA5sJ1KihTuZe-AXX1r8P-8.