Create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

What page is unable to load? Is it My Yahoo and is the explanation:

"Firefox has detected that the server is redirecting the request for this address in a way that will never complete."

That has been going around the past few days and since it works for you in private mode -- where you have completely fresh cookies -- this should help once you are back in "regular" mode (no point doing this in private mode):

(1) Remove your Yahoo cookies (save any pending work first). While viewing a page on the site (can be www.yahoo.com), try either:

• right-click (or on Mac: Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or globe icon in the address bar, click the ">" button, then More Information > "View Cookies"

In the dialog that opens, yahoo.com should be prefilled at the top so you can remove the site's cookies individually.

(2) Then try reloading My Yahoo using Ctrl+Shift+r to bypass previously cached copies of the page.

Success?

It didn't work for me the first time, so I logged in using the main page, then cleared cookies again, and it worked the second time.