You should try step 1, it doesn't matter if you have error message. All it's doing is forcing an actual reload of page itself rather than local cache or stored version. The error message can be the blank screen without any actual code or visible error if that makes sense

1.To force a reload from the Internet, hold down the <Shift> key and press the Reload button.

I guess you're both at a loss :-)

I tried the "Shift and Reload" keys together on yahoo.com, but all that loaded was the same blank white page.

My only other suggestion would be to create a new Firefox profile. In addition to bypassing current add-ons and custom settings, it should have complete fresh settings databases and a fresh cache folder.

Close Firefox and start up in the Profile Manager as described in Managing profiles. Any time you want to switch profiles, close Firefox and return to this dialog.

If http://www.yahoo.com/ works correctly in the new profile, you could continue to diagnose your existing profile, or migrate key settings like bookmarks from your prolem profile to the new one. See Recovering important data from an old profile.

Hope this helps.

Will I lose all my settings by creating a new profile? Have you seen this error before? I still can't believe that yahoo.com is not working after all this. How about uninstalling and re-installing Firefox...would that make any difference?

Will I lose all my settings by creating a new profile?
No, each profile will have its own distinct settings. If in doubt, make a backup of your profile folders (if you open Help > Troubleshooting Information, then click Open Containing Folder and click up a few levels, you can see where they are all located).

Have you seen this error before?
Not on this site.

How about uninstalling and re-installing Firefox...would that make any difference?
Usually not because usually the problem is your profile. However, if the problem is due to a corrupted program component, then it would help.

I know I'm not a tech guy, but the fact that you are a tech guy (I think, right?), and you've never seen this problem on this site makes this even more confusing for me. I will take a look at the profile directions, and try to get to it before tomorrow. Thank you.