Try running it in Diagnose Firefox issues using Troubleshoot Mode to know which extention/add on might be causing it

That can happen if the updater wasn't able to update (replace) all the files in the Firefox program folder (C:\Program Files\Mozilla Firefox\).

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

• Firefox 5.0.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.

Same problem, uninstall + CCleaner tested + restart=> same result Just message is : Platform version 5.0 and min and Max are about 2.0.1 (opposite of title)

this didn't work for me either (uninstall, delete Mozilla folder, reinstall 5.0.1)

You can check if there is a VirtualStore folder.

• C:\Users\<user>\AppData\Local\VirtualStore\Program Files\Mozilla Firefox

The "Application Data" folder in XP/Win2K and the "AppData" folder in Vista/Windows 7 are hidden folders.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

You can also try a custom install in a different program folder (Mozilla Firefox5) to see if that works.