In the last few days In many sites, if not all, trying to go back to previews page(s) (back button), fails.
It usually goes into kind of endless loop. it doesn't go back, and in many cases goes to http://seg.sharethis.com/getSegment.php
On another site, it goes to another page of the site, and "stays" there.
When hitting the back button, the browser tries to go these but falls again on the wrong one.
The only way to see the page you want, is to close the tab and open the site again
Chrome is OK. FireFox is OK. only opera