Are you using Adblock or Adblock Plus? That will be your problem. Disable it and you should be able to fully access the site.
I use Adblock Plus but I don't think thats the cause... well at least not in my case. I have it disabled for WC, but the not being able to submit issue occasionally still occurs. I even uninstalled it to see if that improved things, but alas, it happened now and then. Like is said before, the issue only began with FF 34 - 35, but it's only an intermittant thing, rather than constant, and is easily resolved with a page refresh.