According to Norton's Safe Web website:
Norton Safe Web is a new reputation service from Symantec. Our servers analyze Web sites to see how they will affect you and your computer. Then, using the Norton Toolbar installed on your PC, we let you know how safe a particular Web site might be before you view it. If you need to find out more about how a Web site might behave, we provide more detailed information right here on Norton Safe Web.
To do this, the toolbar has to send the website to Symantec, which then replies with the "safety level", and the toolbar inserts the rating icons on the page. Surprisingly, I can't find any information about what information the toolbar is sending to Norton.
If you don't like the extension, you can always uninstall the Safe Web software, or remove the toolbar from Firefox. Firefox includes it's own malicious content checking (as does Google's search results).
For what it's worth, I much prefer using Microsoft's Security Essentials antivirus/anti-malware over Norton. Security Essentials is quiet and unobtrusive, and so far it's caught everything the web's had to send at me.
I just tried to install the Norton Safe Web Lite toolbar (the free version), and I was able to see (but not copy/paste...) the license agreement, which has a rather large section on privacy. I imagine it's the same or very similar to what you "agreed" to by having their software pre-installed on your laptop.
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