with a recent issue i had, qcdn was also making firefox crash.
but not just qcdn, it was making my entire PC crash if i went to certain websites as well.
the solution was solved by three things
one make sure none of your plug ins and extensions are conflicting with scripts used on qcdn, this can easily cause the problem.
2, if you are using something like Mcafee active shield or anything of the sort, having it scan all files instead of just documents and programs can cause it to malfunction.
the third step, and one that solved my simalar problem was to boot up your pc from the windows disc and do a repair install of windows.
some other options can be to check your graphics card to see if it could use an upgrade to the driver sets, cause it could be a graphics problem too.
these are just a few things i learned about small problems like that.