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recently installed firefox 4.0.1 checks for add on compatibility and will not launch

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firefox 4.0.1 successfully installed. when I try to launch the browser it checks for add on compatibility and freezes at that point. windows reports that the program is not responding. I tried a system restore and reinstalling firefox 4.0 but this does not solve the problem.

firefox 4.0.1 successfully installed. when I try to launch the browser it checks for add on compatibility and freezes at that point. windows reports that the program is not responding. I tried a system restore and reinstalling firefox 4.0 but this does not solve the problem.

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I downgraded to firefox version 3.6 RC 2 and this successfully solved the problem