Problem with a class1 certificate to sign Excel macros
 

I got a class 1 certificate in Firefox and probably did not export in
the right format. I loaded the file in the Certificate section of MMC
(I think in the Root section). Anyway Excel refuses to accept the
signature that I create.

Can some one tell me in what format to export the certificate and
where to import it in MMC Certificate (maybe in the Trusted People
folder according to a message that I found).

If this is not the right forum, please someone tell me.

Thanks
Bernardg