Yes, not caused by the WebRep as it is working for me with firefor 7.0.1 and the webrep. See when I clicked on your image link to view it.

I used to have this problem some while ago, I think in firefox 6.0 when viewing a long set of links in the ‘Show new replies to your posts’ in the forums. I never did pin it down what that was and it eventually came back of its own accord.