The updater wasn't able to update all the files and some were left as older versions.
Do a clean reinstall.

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 6.0.x: http://www.mozilla.com/en-US/firefox/all.html

• Uninstall your current Firefox version.
• Do not remove personal data when you uninstall the current version.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• 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 in the Firefox Profile 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.

cor-el, Thank you very much. Great step-by-step and detail. It worked perfect. I installed 3.6.20 complete, from scratch. No problems! Thank you again, Hovy

You're welcome

I have the same problem. Message says "ERROR, platform version 1.9.2.20 not compatible with Min/Max v 1.9.2.201"

I realize I should follow the steps as above, but I don't know how. I am 83 and took my second computer class last winter, so I am getting better at this and I realize if I'm going to really learn how to do things, I have to ask questions instead of calling upon a granchild to help.

So how do I download "a fresh file" if I can't get on the net with Firefox?

Exactly which files do I remove?

How to I make sure I "Do not remove personal data when you uninstall the current version"?

I have a 5 year old computer running Windows XP.

I am submitting this question using my grandson's laptop, but I don't want him to do it for me, I want to learn how to do it myself.

I thank you very much for your patience towards an old granny. It is very much appreciated!

You can download the latest Firefox 3.6.x version here:

• Firefox 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.html
• Firefox 6.0.x: http://www.mozilla.com/en-US/firefox/all.html

There will be another update shortly (maybe tomorrow) to repair some certificates that were disabled by accident (Firefox 3.6.21 fixed a security issue with a compromised root certificate).

If you choose to uninstall Firefox via the "Control Panel > Add and remove programs" then you see a check box in that uninstall window to remove personal data.
You need to make sure that that box doesn't have a check-mark in it.
You can also first try to only delete the Firefox program folder (C:\Program Files\Mozilla Firefox\) as this issue is likely to be caused by security software that is preventing Firefox from replacing (updating) all the required files.

See also:

• http://kb.mozillazine.org/Profile_backup
• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

THANK YOU VERY MUCH for your prompt reply! I am going to give it a try. I really appreciate your assistance!