www.facebook.com/plugins/like.ph I am getting this url when I hit back button on browser?

This is my work computer, I never go into facebook here. However in the last 3-4 weeks I am getting this url "http://www.facebook.com/plugins/like.ph%22 and/or http://www.facebook.com/plugins/recommen%22 when I hit the back button on my browser. This prevents me from going back to the previous page, I have to look at the list of recent pages visited and then select the one I was in to be able to go back. That's when I see these urls listed as if I had been to those pages. Is anybody else having this problem? Is this a virus? Thanks for the help!!