[plug] Changing User agent in Firefox

[Arie Hol]

Can anybody tell me if it is possible and if so, how to change the 
default user agent string in the Firefox browser.

I need to access some web sites that are heavily biased towards Internet 
Explorer, and would prefer to be able to make IE the default (but only 
while I need to access these sites)

I know how to change the User Agent string for the current session, but 
it reverts to the current default every time I restart Firefox. 

TIA

Regards Arie
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