I have no problem with Firefox, so the problem is likely on your side rather than on PD.
Have you installed some browner plug-ins on your Firefox and Chrome that help you to block sites or contents of sites, something like BlockSite, NoScript, FlashBlock, etc?
You may try to disable all plug-ins, to see if it works. If it does work then, you can try to re-enable the plug-ins one by one to find out which plug-in is causing the problem.
It is on site side, I have to Flash block etc.. and had to use Incognito Mode on Chrome to access, and one day, it just fixed itself.