> This is exactly what the Google Container add-on for Firefox protects against. It stops Google from tracking you across the web because your Google login does not exist when you visit other websites.

I don't think that it does. I mean, it does help a little, but if you have Firefox with this add-on installed and visit websiteA which pings google's server and loads their JS which fingerprints your browser they have your device logged, the fact that you visited websiteA logged, your IP address logged, and a timestamp logged. When you visit websiteB 5 hours later (in a different tab, window, or session) and that site also pings google's server and loads their JS they get all that same information again and Google has successfully tracked you going to both sites.

These containers aren't useless, but they aren't preventing Google from tracking your online activity either.

Your best bet is to configure Firefox to not allow javascript (at least not by default and not got any domain owned by Google), to block all google domains at your edge, and never log into a google product. At that point, google isn't tracking you and you have no need for the add-on. That assumes that you're on a PC. If you're using an android device you might as well accept that any website you visit will be tracked by google no matter what else you do.