Just started seeing this about three days ago:

Opening or refreshing any page on hdforums.com triggers a popup warning that facebook.com is trying to open a site in my trusted sites list. Click on either "OK" or "Ignore" and it goes away, then pops up again in the next page load or refresh.

I had added hdforums to my Trusted Sites list in IE. When I deleted it, the warning popups went away.

Looks like hdforums new arrangement with Facebook is doing something to the hdforum page load process that make IE think it is in the facebook.com domain (???).