A facebook employee explained me how tracking works. Its not the email address Meta is concerned about. Its the IP, device identifiers and location. Meta doesnt care about the email at all apart from sending you emails for notification. Even with a fake email they exactly know who you are. Let's say you visit CNN.com which has facebook tracker. Facebook has the IP and the device identifiers. Now you login with fake email account on Instagram, facebook knows that's the IP ans the same device hence it "must" be the same person That's how facebook creates shadow profiles.
Does Firefox containers hide your IP, device info and location?
you can use firefox containers with container proxy to have different ips on each container. that said i run wireguard on my router itself so all the devices are behind vpn.
https://addons.mozilla.org/en-US/firefox/addon/container-proxy/
as for location, changing ip also changes your geolocation. there is also the location reported by your browser which you can change in about:config but this isn't provided unless you give permission to the site asking it.
as for device info, each container is like having a separate firefox install. all the cookies are separated and isolated.