@hugh this wouldn't be services, but people you know who have your actual email address and then give the FB app access to their phone contacts when asked - I'm out of the loop but the app definitely used to do this.
It'd be pretty simple to find links then if they look at their own userbase and find your contact info in common between two groups, even if you don't actually have a profile yourself.
No browser trickery needed at all when people hand stuff over.