Making Firefox 2 default browser in Dapper

[Nikolai Razouvayev]

I installed Firefox 2 on Dapper and it works as a default browser in all 
respects except when I'm trying to open an html page or a saved link 
locally, Firefox 1.5 starts instead. How do I make Firefox 2 start on 
these actions rather than Firefox 1.5? I tried changing it through 
Preferred Applications by typing in the Command field 
/opt/firefox/firefox %s (this is where I installed firefox 2) but it 
doesn't work.

Any help please?

Thanks