I don’t think facebook can snoop on firefox these days. Firefox has already isolated all third party cookie and site content by default:

• https://blog.mozilla.org/en/products/firefox/todays-firefox-blocks-third-party-tracking-cookies-and-cryptomining-by-default/
• https://blog.mozilla.org/en/mozilla/firefox-rolls-out-total-cookie-protection-by-default-to-all-users-worldwide/
• https://old.reddit.com/r/firefox/comments/116r2vm/question_about_using_firefox_browser_and/

So if you are using container tabs to prevent cross-site tracking, then they probably only adds fingerprinting vector (probably a rather small one though, as these extensions do not change the contents of the site).