That file editor seems to work in Firefox. I just tested the save/open functionality.
It's not using the File System Access API, on Firefox it uses <input type="file"> for file-picking, and the save just downloads it. It's not synchronizing anything with your filesystem.
It just downloaded the file on my firefox.
It's not using the File System Access API, on Firefox it uses <input type="file"> for file-picking, and the save just downloads it. It's not synchronizing anything with your filesystem.