Hi! Thanks for the review! :)

You are right, SSS doesn't support Firefox Sync currently. Sorry! I had implemented it but found a bug in Firefox (which I reported here: https://bugzilla.mozilla.org/show_bug.cgi?id=1423744) that could cause problems if the user's icon images exceed the storage limit, so decided to postpone it. It will come eventually, with the bug or not. ;)

Meanwhile, you can try the "Storage & backup" section and export your settings to a file. Then on the other computer you can import the file. I know... it's not as convenient... I understand your criticism. :)