When you install Facebook Container, the extension will start by deleting the cookie that keeps you logged into Facebook. Next time you visit the site, it will appear in a blue-highlighted tab and you can log back in as normal.
Following a link from Facebook to a different site will cause it to open in a new tab outside the container, and clicking Share buttons on other sites will open them within the container. Bear in mind that these buttons pass information about the site you arrived from to Facebook.
Because you're only logged into Facebook within the container, sites and apps that require you to log in using your account won't work. Neither will embedded Facebook comments or Like buttons on other sites.
Pressing pause on advertising
Mozilla is one of several companies that have suspended advertising on Facebook following the news that data analysis company Cambridge Analytica had harvested data from 50 million people without permission.
We are encouraged that Mark Zuckerberg has promised to improve the privacy settings and make them more protective," Mozilla said in a statement on its company blog. "When Facebook takes stronger action in how it shares customer data, specifically strengthening its default privacy settings for third-party apps, we’ll consider returning."