I is happy now.
Saturday two weeks ago, my geriatric, worn-out graphics card, a Radeon HD 7770 by MSI, finally gave the ghost up. That meant that my tower was down.
But that also meant that I finally had a reason to upgrade it. 1GB of VRAM is too little for the #
FirestormViewer.
This week, I got some replacement RAM for the machine. 2x4GB DDR3-1600 + a salvaged 4GB DDR3-1333 wasn't optimal. Now I have 2x8GB DDR3-1600. Come to think of it, I could toss the other two 4GB modules back in...
And yesterday, I picked up a "new" graphics card. A Radeon RX 590 by Sapphire with 8GB of VRAM, probably ample for two Firestorms.
I've only just started testing, but the machine seems to perform better with ambient occlusion, full shadows and full water transparency on now than it did with all that stuff off previously.