that my Stylish editor was completely broken. 
This left me feeling very
because I was doing a demo of my custom FF GUI to an absolute computer ignorant idiot-savant who accused me of stealing somebody elses work; I'm insufficiently intellectual to derive the whatnots, and the all-that's, that are necessary to come up with such a cool theme as what I had demo'd. So I intended to prove it by showing the Stylish code and yet, wait for it....The Stylish editor was totally borked. Oh, sure! How convenient for you that its now borked so you can't prove you're actually smart enough for them to be impressed.
After much fiddling around
with various knobs, switches, and levers: I determined 
the NoScript extension is wholly at fault.I determined this by disabling the current version of NS - v2.9.5.1 - and ascertaining that the current version of Stylish is wholly functional with all other current extensions enabled; a Stylish user had complained about the Stylish editor becoming broken recently and declared that the prollem was solved by disabling AdBlocker. An NS extension user, obviously, has absolutely no use for AdBlock, therefore I never considered that NS could even remotely be the source of all my travails.
So, all that, notwithstanding, and what not, I'm going to assay which of the previous versions of NS is simpatico with current iterations of FF base-code and NS in conjunction with compatible extensions / appearance plug-ins.
I'll keep you posted which way my divining-rod twitches.
