What sort of problems so you run into with newer service packs? You do know that by not updating Windows or Firefox you are leaving yourself wide open for attack with MANY known security holes? Not to mention stability and performance issues. I'd suggest you try the following to make sure your PC is in General good health before troubleshooting:

Scan for Malware: This is possibly the trouble you have updating Windows. Try reading Troubleshoot Firefox issues caused by malware and run the programs recommended there.

Update Windows: Run the updater to install all updates, some updates need to be installed before a Service pack can install. Restart your PC and run update again until you have installed all available updates.

Update Firefox: Update Firefox to the latest release

Now test for issues again, and let me know if anything changed :)

The one time I tried to install XP SP 2, I got caught in an endless bootup loop - get through DOS-style screens OK, enter Windows, desktop comes up, Windows shuts down and computer restarts before bootup complete, back to DOS-style screens, etc. I had to do a system restore to get my computer running again. The tech I spoke to about that problem said there likely was an incompatibility with my machine somewhere. Oh, and I do use malware and virus scanners regularly.

I do not know how all that can keep Firefox from recognizing one TrueType font in my Windows/Fonts directory when it recognizes all other fonts there.

I don't think that tech knew what they were talking about, your machine will run Service Pack 3 just fine. Try to update Windows again now and then Firefox. I can't really give you any additional support until you've done that as you are running a know buggy operating system we don't support anymore and a known buggy version of Firefox

If I couldn't install XP SP 2 properly, how can I install XP SP 3 properly?

And besides which, as I said, FireFox recognizes all the other TrueType fonts I have on my system. It's just this one font (News Gothic BT) it cannot recognize. If this was a FireFox bug, I'd expect the browser to have problems with other TrueType fonts as well.

I have a bet that the service pack failing was a fluke, and if you were to try again (disable your antivirus, make sure you leave the computer alone while it's being installed, etc. It should work.

Note that the font drop list consists of several sections (sans-serif, serif , ordered uppercase and lowercase), so you may have to scroll down further if you do not see it.

I've installed the font and I'm seeing it in the first sans-serif section under NewsGoth BT, so the font is working for me in Firefox 16 on Linux. If that font works with other programs on your Windows XP OS then it should work in Firefox as well.

Tylerdowner - I tried again to update to XP SP2, and this time the installation went OK, but afterward, Windows couldn't validate my internet connection, keeping me from using the net, so I had to revert to SP1 again.

cor-el - I'm well aware that the drop-down list is divided into several sections, and News Gothic BT isn't in any of them.

Have now successfully upgraded to XP SP 2 and then to SP 3, and updated FireFox. News Gothic BT still won't show up in the drop down list.