I had the strangest thing happen on one of my clients PCs today.  I was working on their new PC and they were showing me how they kept getting javascript errors on their yahoo mail website when trying to print or open links in the email. I logged into their yahoo mail account on my pc and was able to click on the links and print just fine.  I tried going back to their Yahoo Mail account on their computer and I couldn no longer login to Yahoo Mail.  It kept throwing me back to the login page even though at the top right hand corner of the screen it showed that she was “signed in”  I tried several things, including running malwarebytes and hijackthis, which both found a couple of BHO’s and malwarebytes found a couple of trojans.  After infections were removed, the Yahoo Mail problem still persisted.  I was not able to fix the problem, but rather installed Google Chrome and was able to login to Yahoo Mail as well as click on the links in their mail and print.  Strange.  If anyone reading this post has ever encountered this particular problem before, feel free to comment.