Example files for trying out Save Back to File from DOM https://addons.mozilla.org/en-US/firefox/addon/save-back-to-file-from-dom/:

How to use: Store (save) these files on your local file system (disk). Open them from there. Makes changes (by using your mouse to click or to drag). Save back to file by using Save Back to File from DOM. Open again to see changes have been saved.

Idea and first implementation by Leo Baschy and Hans Baschy.