When you open the affected links in your browser you will see a note at the end:
"Es tut uns leid, aber die von Ihnen angefragte Datei kann zurzeit nicht heruntergeladen werden. Bitte
[Please Register or Login to download file] und informieren Sie uns über dieses Problem. "
Kontaktieren Sie uns will give you the chance to report the problem to FF - I already did but if more people do the same the links should be working again in a few hours.
Seems that FF did some server works and messed something up.