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"what happened:TypeError:Components.classes['@mozilla.org/extensions/manager;1'] is undefined" This message prevents the web from loading until I hit OK. Started happening when I upgraded to 4.0 Can you help?

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Last week I upgraded from 3.6.15 to 4.0 and got this error message every time I tried to get on the web. Uninstalled and reinstalled twice but will not go away. I even uninstalled and went back to 3.6.15 but had the same problem. This message also comes up if I have a link to go to another page.

Last week I upgraded from 3.6.15 to 4.0 and got this error message every time I tried to get on the web. Uninstalled and reinstalled twice but will not go away. I even uninstalled and went back to 3.6.15 but had the same problem. This message also comes up if I have a link to go to another page.

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Do you have that problem when running in the Firefox SafeMode?
A troubleshooting mode.
You can open the Firefox 4.0 SafeMode by holding the Shft key when you use the Firefox desktop or Start menu shortcut. Or use the Help menu item, click on Restart with Add-ons Disabled... while Firefox is running.
To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut to open it again.

If not, see this:
http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes

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The shift key idea worked . Thanks