I'm having a similar problem.
When using IE8 I noticed that it took 2 clicks on the back button to actually go back to the previously visited FT page. I checked the back button's drop down and saw that a link to facebook was being inserted as the previous page. This is not the case when I use Firefox where the back button works as expected.
Not sure how Facebook is getting into the chain of visited sites (I NEVER use FB) and why it's only happening with IE8.
Any thoughts?