Ok, I just found out what the problem is: This feature gets installed on your system when you install GAP (the GIMP Animation Plugin). I've used GIMP and GAP for so long I wasn't aware that the Filter All Layers came as a part of GAP. My apologies for the confusion. I'll modify the tutorial later to state this. Please keep in mind that if you don't currently have GAP installed and you're afraid to because of its difficulties, go ahead and install it so you can experience some good things! JKM, since you were able to do my Animated Snowfall tutorial (nice job, BTW!), I would think it would be installed already on your computer. This is really strange now.
Sorry for the confusion, everyone.