On Android at least, Firefox PWA’s don’t seem to support registering system-level things (like ‘Share To’ handlers) - you need to use a Chrome PWA for that…
No Japanese :(
For me:
browser.ctrlTab.recentlyUsedOrder: False
browser.tabs.insertAfterCurrent: True
dom.popup_maximum: 100
browser.download.improvements_to_download_panel: False
This show keeps growing on me!