I use Firefox with the official extension Firefox Multi-Account Containers. I use an exclusive container for the Meta websites Facebook and Instagram. I.e., all their domains will open in this container, and no other domains will open in this container. The idea is that Facebook cannot track me outside of their own domains.
Thus I was surprised to find multiple ads in my Facebook feed for a product that I had just come into contact with minutes before on a different domain.
Must I have violated the above stated principles somehow and leaked data between containers? E.g., is my usage of WhatsApp Web outside of the Facebook/Instagram container the issue? Can using the "Firefox Sync"-ed (single-container) Firefox Mobile on my phone be the issue? Or is there a way that Facebook could track me across containers?
