This extension helps you control more of your web activity from
Facebook by isolating your identity into a separate container.
This makes it harder for Facebook to track your activity on other
websites via third-party cookies.
Rather than stop using a service you find valuable and miss out on
those adorable photos of your nephew, we think you should have
tools to limit what data others can collect about you. That
includes us: Mozilla does not collect data from your use of the
Facebook Container extension. We only know the number of times the
extension is installed or removed.
In other words, Firefox is now treating Facebook as malware that you need to be protected from.