I’ve used regular Firescoff for firestain protection on silver during soldering with mixed results. I recently discovered there was a product called Firescoff MA which you spray on metal during casting that supposedly reduces oxygen uptake and thereby reduces porosity.
Have any of you used this and if so, any good?
It’s pretty expensive and precious little info available with the firescoff.com website being idled for 2 years and counting.
Here’s my two-cents about Firescoff. YES, it prevents firescale. But with some caveats: first, the learning curve is pretty crazy. You have to spend time to figure out how to apply it properly. And even when you get to be expert at it (meaning, not wasting it because it’s easy to over-apply it), you still need quite a bit and let’s face it, this stuff is expensive. The downside, and why I will no longer be using Firescoff for any pieces that require more than one solder joint: Things MOVE, because Firescoff is not just a firescale preventative, it’s also a flux, therefore, every time you coat your piece with it, it’s also acting as a flux, thereby other soldered joints will flow. Ask me how I know this 
I recently did a couple of pieces with no less than 7 joins, and each time I soldered, every join flowed. SO, while this stuff is so good for say, a shank (one joint) or perhaps even two joints where you can easily ochre the prior joint, it’s not great for pieces with multiple join areas. I guess you could ochre them all, but that sounds like a massive nightmarish ball of horrible yuck. I do have a few pieces in my collection with just a couple of joins, so, I will reserve my Firescoff for that. All else, I will use my charcoal block, boric acid/alcohol, and the flux of my choice. I would rather scrub a dub dub any firescale (I never get it too bad anyway) than deal with moved joins that I so painstakingly cut, filed, and soldered. In my opinion, the best a silversmith can do is try the best they can to prevent firescale, but to also embrace it as part of the process. As long as we are doing all we can to prevent it, it makes no sense to get bothered when it does show up. It’s like death and taxes. Unavoidable, but deal-with-able. lol.