First, make a backup of your computer for safekeeping. To back up Firefox, see Backing up your information.

Next, try starting Firefox in Firefox Safe Mode. Be careful not to "reset" anything permanently if you didn't back up.

Does that run normally?

If so, you could disable your add-ons and just re-enable the most critical ones.

If not, try creating a new (blank) profile: Managing profiles.

To move key settings like bookmarks from your damaged profile to the new profile, see: Recovering important data from an old profile.

Hope this helps.

Thanks for the speedy reply! Before I attempt your key steps, can you please tell me HOW to "make a backup of [my] computer for safekeeping"? I backup My Documents by copying them to an external hard drive, but don't know how to make a backup of the computer. No rush - after 12 hrs. at the screen studying support info, will probably not attempt pursuing the "cure" tonight!

If you follow the link for "Backing up your information" that describes how to back up your Firefox information.

You should be careful with doing a system restore because that often gives more problems then it cures and can cause the Firefox installation to get corrupted (some files get restored and others not).

Do a clean (re-)install:

• Download a fresh Firefox copy and save the file to the desktop.
• Firefox 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.html
• Firefox 4.0.x: http://www.mozilla.com/en-US/firefox/all.html

• Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer.
• Do not remove personal data if you uninstall the current version.
• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere (not in the Firefox program folder) and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

Thank you very, very much for providing the simple, concise directions that solved my problem! After sorely missing Firefox 3.6.16 for a month, today I finally worked up the courage/got desperate enough to attempt (with much trepidation!) the download and re-installation.

Step 4 was a bit of a challenge, but following Uninstall directions in the 3.6.16 Release Notes advising removal through Control Panel appears to have preserved my Profile and worked fine. Was not quite sure how to go about properly removing the Firefox program folder, so I opened Local Disk (C:)/Program Files/ and deleted (to Recycle Bin) the Mozilla Firefox folder – and am keeping fingers crossed that that was the correct method.

It was quite a satisfying thrill when Firefox 3.6.17 opened, but very distressing to note that “Firefox 3.6.x will be maintained with security and stability updates for a short amount of time. All users are strongly encouraged to upgrade to Firefox 4”. Sadly, it seems all things Internet seem to be evolving towards mobile devices, social networking, and the ability to sync all the fancy new toys – and getting much to complex for us old dogs who don’t learn new tricks easily, or need them for that matter.

Thanks again!