FF 13.0.1 pop up windows problem

When watching Sky Go on my laptop, FF allows a pop up window but won't run the video. I have checked that Tools/Options/Content has the "block pop up windows" box unchecked. But the problem remains. Works OK in IE9.

The fix for this was an interesting one. I run "Ghostery" in Firefox. On the Sky Go page Ghostery was blocking "Omniture" . When I removed the block, the pop up window worked as it should.