How to import and export ssl keys/certificates in different computers?

Firefox
Step 1: in computer 1:
Firefox: Select "Tools" ->"Options"-> "Advanced" -> "View Certificates", choose the "Your Certificates" tab and locate your certificate from the list.
Export the certificate.
Step 2: in Computer 2:
The same process as 1 except the last step to import the certificate file created in step 1

Step 1 can also be used to backup your certificate keys.