Was just coming back to this thread to say I use the Multi-Account Containers extension to isolate my Facebook, YouTube, Twitter, and Google Search sessions from the rest of my web browsing, and I highly recommend it.

The terminology is a little confusing: Containers or "Container Tabs" is a session-management tool that's baked into Firefox, while Multi-Account Containers is an extension on top of that that allows you to automatically sort specific domains into containers, so when I open e.g. a YouTube link it automatically appears in a YouTube container, which knows nothing about my Google account. IMO the functionality of the extension (which was written by Mozilla) should be added to the browser itself.

https://addons.mozilla.org/en-GB/firefox/addon/multi-account...