Two thoughts:

(1) Firefox uses your system-level ClearType and other font anti-aliasing settings. Unlike IE, it does not a separate ClearType setting. Normally, the Windows 7 default settings work.

(2) Fonts often look better with hardware acceleration enabled. Your "More System Details" show that setting to be disabled, perhaps because Firefox was crashy with your current graphics card drivers... Do you recall changing that?

2) re: hardware acceleration, yes, I think I saw in FAQs that disabling might resolve this issue. I can turn it back on, but it had been on ... 1) I'm not sure what to do with that. I don't notice font display issues in other apps on this PC. Thanks!

Firefox isn't always able to use hardware acceleration. In some cases, because a version of the graphics driver causes crashes, Firefox will refuse to use hardware acceleration until it is updated.

If you're inclined to consider updating, I suggest using your manufacturer's website for those updates instead of Microsoft's update website. (Maybe I'm just paranoid from the old days...)

I checked the hardware acceleration option in FF options, and went to the display properties setting to enable hardware acceleration there too, but it's grayed out. Turns out the Intel HD Graphics software controls that and it's not user definable. The display driver is up to date, so I'm not sure what else I can do. Suggestions?

Solved! ClearType font was not enabled. I enabled and the problem is gone. Thanks for your help.