Firefox won't start

In Firefox v1.0.7 (Win2k), I apparently closed the browser previously 
while the User Agent was set to spoof as Internet Explorer, with the 
result that I can't start the browser anymore -- It tells me that I 
should use only Navigator plugins in this browser.
 
Please tell me how to go about fixing this.
 
-- 
Stan Goodman
Qiryat Tiv'on
Israel