Made since Firefox 57 to replace the earlier Save Back to File from DOM
https://addons.mozilla.org/en-US/firefox/addon/save-back-to-file-from-dom/ .

Install

• License: BSD 2-Clause "Simplified" License
• Weekly downloads: 1
• Average daily users: 42
• Rating: 5/5 of 2 ratings
• Created: 2018-01-04 06:23:42
• Last updated: 2019-05-07 21:20:14
• Homepage: https://github.com/srguiwiz/download-dom-xpi
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/download-serialized-dom/
• API: download.dom.id@nospam.nrvr.com