Solution (for me) to the "Thumbnails Not Enlarging" bug
Adblock Plus is the culprit to our problems (as found by Kiteman, his find pointed me in the right direction). Simply updating your filter subscriptions will solve the issue.
In Firefox: click on Tools, mouse-over Adblock Plus, select Filter Preferences, click Actions and choose Update Filters. All that's left is to refresh the page and all should be fixed (it was in my case, mileage may vary).
I hope this helps you guys and gals who have this issue.