Well, Chrome obviously does if you’re ‘signed in’ to Google and haven’t turned off their sync settings… which I imagine is the most common end user path, and chrome is the most popular browser.
https://www.google.com/chrome/privacy/
Are you saying that Google is using their control of the user agent to specifically tie a Google auth cookie to an individual third-party-context web request even when third party cookies are blocked? If so, that would be a major scandal. What evidence do you have that this is the case?
So are Firefox accounts but they probably don't have the numbers to engage in any particularly egregious behavior.