Try the following:
In IE 10, include the SEPM to your Trusted sites (Internet options in Windows). Try to access the SEPM again. At the SEPM logon screen, click on "Certificate error" in the address line. Then you should be able to import the SEPM certificate.
In Firefox, go to the browser settings (Advanced > Certificates > Servers > Add Exception) and import the SEPM certificate from SEPM_IP_address:8445.
HTH!