A Google search turned up that I'm not the first crazy person to ask this question!
It turns out that Firefox uses something named "chrome" in its programming, but have no idea if it's related to "Google Chrome" or anything.
Anyway, on a whim, we uninstalled Firefox and did a complete re-install... to no avail. The script pop-ups when trying to do anything in "Firefox/Tools/Options" continue, as does the "JIT Debugger", etc.
No, I haven't uninstalled Java... yet.
I'm going to download and install SP3 tonight and see if that fixes anything.
Really can't afford a new laptop right now, so need to keep trying to repair this one for now.
The next tribulation will be to completely reinstall XP, but I have a dozen things to do before I'll be able to mess with that.
I don't know why these problems are so elusive this time around, but my patience is really being tested, and life sucks as it is, so this PC is on borrowed time for target practice if it doesn't straighten up...