Search on forum, someone have already do that…
This download all root certificates.
http://forum.mikrotik.com/t/updating-ca-root-certs-regularly/144990/1
If you want install only one root cert (DigiCert Global Root G3), use only first part, with correct certificate:
/file
print file=DigiCertGlobalRootG3.txt
:delay 1s
set DigiCertGlobalRootG3.txt content=“-----BEGIN CERTIFICATE-----\r
\nMIICPzCCAcWgAwIBAgIQBVVWvPJepDU1w6QP1atFcjAKBggqhkjOPQQDAzBhMQsw\r
\nCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3d3cu\r
\nZGlnaWNlcnQuY29tMSAwHgYDVQQDExdEaWdpQ2VydCBHbG9iYWwgUm9vdCBHMzAe\r
\nFw0xMzA4MDExMjAwMDBaFw0zODAxMTUxMjAwMDBaMGExCzAJBgNVBAYTAlVTMRUw\r
\nEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20x\r
\nIDAeBgNVBAMTF0RpZ2lDZXJ0IEdsb2JhbCBSb290IEczMHYwEAYHKoZIzj0CAQYF\r
\nK4EEACIDYgAE3afZu4q4C/sLfyHS8L6+c/MzXRq8NOrexpu80JX28MzQC7phW1FG\r
\nfp4tn+6OYwwX7Adw9c+ELkCDnOg/QW07rdOkFFk2eJ0DQ+4QE2xy3q6Ip6FrtUPO\r
\nZ9wj/wMco+I+o0IwQDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQEAwIBhjAd\r
\nBgNVHQ4EFgQUs9tIpPmhxdiuNkHMEWNpYim8S8YwCgYIKoZIzj0EAwMDaAAwZQIx\r
\nAK288mw/EkrRLTnDCgmXc/SINoyIJ7vmiI1Qhadj+Z4y3maTD/HMsQmP3Wyr+mt/\r
\noAIwOWZbwmSNuJ5Q3KjVSaLtx9zRSX8XAbjIho9OjIgrqJqpisXRAL34VOKa5Vt8\r
\nsycX\r
\n-----END CERTIFICATE-----”
/certificate
import file-name=DigiCertGlobalRootG3.txt passphrase=“” name=imported-ca-cert_DigiCertGlobalRootG3
/file remove [find where name=DigiCertGlobalRootG3.txt]
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so, after “installation” check the fingerprint of certificare with what is written inside Firefox.