Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox including hardware acceleration of graphics. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

Yeah, this seems to take care of those issues! Do I need to run Firefox in safe mode from here on out?

It's hard to live in Safe Mode because you can't use any extensions. Let's start with hardware acceleration. Sometimes Firefox is incompatible with your graphics card driver. To work around that, you can try disabling hardware acceleration, then start Firefox normally.

"3-bar" menu button (or Tools menu) > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

This will take effect after you exit and start Firefox up again.

Any improvement? If that makes no difference, it could be an extension or a customization (e.g., in a userContent.css file), or...

Yeah, this seems to be working just fine now. Thanks!

Is there anything else I need to do?

I think that's it. Your graphics card drivers may update periodically, either from Windows Update or other scheduled updates. When you notice that happen, try re-enabling hardware acceleration to see whether it works. It also would be worth a try after Firefox 33 is released (in October, I think). When it works, you get improved performance on 3D graphics and font smoothing. (Probably not a big deal, but...)

Awesome, thanks again!