How to export a personal digital certificate from Mozilla on Linux

1. Select Edit->Preferences from the menubar.
2. Select Privacy & Security->Certificates and click Manage Certificates:

   

3. Select your certificate and click the Backup button.
4. Provide a filename and click Save.
5. Enter a password. You will only need to use this password for a short time, but you should still select one that is reasonably secure.