Mozilla recently updated Firefox to support a 64bit system only. As the Slingbox works on 32bit, this has caused some complications; however, we are working diligently with them to fully resolve the issue. In the mean time, they have provided this work around:
•In the address bar type: "about:config"
•A message will pop up for dangers of the these options agree to them.
•Search for "xpinstall.signatures.required". It should have a value of True.
•Right click on "xpinstall.signatures.required"
•"Toggle" the value will change to false.
I hope this helps!!
Sling Media Technical Support