Mozilla Archive Format (MAF) and UnMHT don't work with Firefox after Version 56 or with other browsers. Legacy extensions, such as MAF and UnMHT, were able to access internal functionality within Firefox to support their operations. This is not possible for new extensions that have to use the new WebExtensions API's. Also, new extensions cannot access all of the resources that were loaded when the page was loaded by the browser, so these resources have to be reloaded.