+1 just for getting 'disclosure' right...
If it is a hash it could still see if a certain website was visited. Is this right?
How do I disable this in Firefox? Is this the section about "Content Blocking"?
Firefox docs are on https://wiki.mozilla.org/Security/Safe_Browsing and offer a range of config knobs.
"Each site you visit is checked against the Safe Browsing list on your system. If there's a match, your browser sends Google a hashed, partial copy of the site’s URL so that Google can send more information to your browser. Google cannot determine the real URL from this information." -- https://www.google.com/intl/en/chrome/privacy/#safe-browsing...
There's no way Firefox would be ok with sending all their user's visited URLs to Google.
(Disclosure: I work at Google)