Here is a some design documentation for the safe browsing add-on: http://wiki.mozilla.org/Safe_Browsing:_Design_Docu mentation

Here is the Bugzilla bug for turning on the feature. Remember that you have to copy and paste the link into the address bar because Bugzilla blocks slashdot. https://ancillary-proxy.atarimworker.io?url=https%3A%2F%2Fbugzilla.mozilla.org%2Fshow_bug.cgi%3Fid%3D32929 2

From what I understand, the idea is to make the feature an extension that is installed by default, kind of like the talkback error reporting tool. In "normal mode", the extension will make decisions on phishing sites based on a blacklist file that is downloaded from an update server, and every address that you visit will NOT be sent to Google or Mozilla for verification. If the user goes to turn on Enhanced Mode, a warning dialog will pop up telling them that information WILL be sent to Google or someone else, for the purposes of finding new sites to add to the blacklist files and online blacklist database. I don't think that enhanced mode will be turned on by default, but there are still a lot of things that are undecided.