Many people are reporting unexpected sign-ins in recent days, including the "unknown" connection. (https://old.reddit.com/r/firefox/comments/1hq7tli/attempted_login_to_mozilla_account/)

The globe icon typically indicates a web connection instead of a Sync connection. If there isn't a device (computer or mobile) fetching your data, the incident *probably* did not result in a leak of data but unfortunately, I don't know how to be sure of that.

That said, I don't know why you can't disconnect it. Hopefully someone who knows what is going on will chime in.

The Firefox Account has been called Mozilla Account since early November 2023 even though links like accounts.firefox.com is still being used.

I wonder if all of these reports I have seen in last days were actually others managing to sign into their Mozilla Account or if they were actually reports of failed attempts whether by accident or intentionally trying to login.