This 'back' button... is this the browser (e.g. IE9) back button? Or a button imbedded in the CN article?
Are you a facebook user? Do you have your own website where you may have added a Facebook like button? Reason I ask is that a bridge or link between your website and Facebook is created in the background when you add Facebook Like buttons to your website. If this is a possibility you might try searching the internet for solutions to this problem. Problems similar to this are fairly common. Common enough that they are being discussed in other forums. Since you have this issue in other sites besides CN, you may have some browser script that is always running in the background. Take a look at the following for general information.
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http://personalweb.about.com/od/facebookconnect/a/Add-Facebook-Like-Button.htm
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https://developers.facebook.com/docs/opengraph/
That said, I have experienced browser issues after using Facebook, but nothing like yours. My IE app on my PC sometimes becomes very sluggish, while other apps are okay. After I cleanup my computer's temporary internet files and cookies I never have any further trouble. Unfortunately the latest Windows XP service packs and Windows 7 do not allow access to clean these up on your own like they used to back in the day. To clean up my PC I have been using Norton 360, which comes with a complement of utilites to keep the PC running smooth. (BTW, I don't work for Symantec or sell their products. Just use them.)
There are few other possibilities that come to mind but probably not ones that would cause your problem.