Just heads up here. I was able to restore it partially on Windows using https://www.shadowexplorer.com/downloads.html (which is, btw, a great tool!)

You'd be looking for a file C:\Users\YOUR_USER_NAME\AppData\Roaming\Mozilla\Firefox\Profiles\YOUR_PROFILE\containers.json

and also ...\YOUR_PROFILE\browser-extension-data\@testpilot-containers

Thanks, you just saved me a headache.