LibriumArcana.Games

as my starting site? Mozilla 41.0.1 on Win 7 Pro, and so far all attempts to remove it (including trying to excise it from the registry the hard way) have either not worked or made matters worse.
It doesn't show up in software on the Control Panel, simply overwriting the starting/home page in the FF settings doesn't work, while this is so far a mild nuisance (I usually have FF start on a blank page so who cares if it starts on the mystartsearch one as long as that's the 'only' thing it does?) Regardless how harmless it appears to be, it annoys me.

Sounds like your PC has spyware installed, or something worse.

If you don't have it already, get Spybot S&D (from the site safer-networking.org, as quite a few of the other sites have unofficial versions at best), update it, and then let it scan your PC. This should resolve the problem, though the scan could take a while.

Throwing Spybot at it was the first thing I tried.

Then what else have you tried?