First of all - what are the manufacturers of these masks doing sending off masks that are not properly cleaned of a manufacturing residue that keeps them from working as designed. This is just garbage. Where are the "class action suit lawyers" when you need them.
Secondly - Follow the manufacturer's recommendation. If they say flame, Bon-Ami, Toothpaste or cowpies - just do what they say.
Last of all - I'd ask the LDS where I bought it and then do it with them, or let them do whatever. If they said, "Flame it" - I'd take it to them and let them do it, and if they ruined it, they'd replace it. I'm certainly not going to listen to someone who will take no responsibility if I ruin my mask through some lame-brained idea.
In the meantime, as I said before, I've used toothpaste for my masks, my family's, and others. Unless something has changed drastically, and I would expect this to be brought to our attention by the manufacturer/LDS, I will keep on with the toothpaste.