I'm wondering what's different on your set-up, Tony. I am running FF17.0.1 on Windows 7 and Windows XPsp2 on another machine and haven't seen the warnings since the first day. Is there something in the history or cache that could be triggering the warning?
I saw it the first day...then the other day when I cleared all cookies(was having an unrelated issue of remaining logged in). Any way after clearing cookies it came back for seconded time. Once I told it, it was not a bad site, it has never came back up. This was on FF 18beta. I installed FF19 Aurora, last night just to experiment with it mostly, and not seen it at all on FF Aurora.
Unrelated note: Aurora is lots smoother and faster than regular FF.