You can view Certificate contents in Firefox
(Tools -> Options -> Advanced -> Encryption -> View Certs -> Yours/Authority/etc
-> <cert> -> View -> Details -> Certificate Fields -> Public Key
)
If you can export to PEM, you can convert that to PKCS12
# export mycert.pem as PKCS#12 file, mycert.pfx
openssl pkcs12 -export \
-out mycert.pfx -in mycert.pem \
-name "My Certificate"
Update: Examples of using OpenSSL
Generate a self-signed certificate
$ openssl req \
> -x509 -nodes -days 365 \
> -newkey rsa:1024 -keyout mycert.pem -out mycert.pem
View it's contents
$ openssl x509 -in mycert.pem -noout -text
View the PEM file
$ cat mycert.pem
-----BEGIN RSA PRIVATE KEY-----
MIICXAIBAAKBgQDa6JQOLkwoIGhTvcTSYX68Ddaq4hGk/61RSVELaVFJTNQYPB86
…
aPj0KoeFJ04/sLcZNZwGcC93rNA66xTICLtGbBXlM1U=
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
MIICxTCCAi6gAwIBAgIJAOaxxgLFlypwMA0GCSqGSIb3DQEBBQUAMEwxCzAJBgNV
…
tz0TMEYxbGIscZbxeJxoK6pe5tOwXtdjStlcITzksdPV5rLp84aeJl4=
-----END CERTIFICATE-----
Note that whilst a PEM file can contain both private key and a certificate, the private key isn't part of the X.509 certificate.
If the PEM exported by FF lacks the BEGIN and END markers around the Base64 encoded data, OpenSSL can't read the PEM file.
Here's CA certificate I exported from Firefox (*viewed in e.g. notepad)
-----BEGIN CERTIFICATE-----
MIIDdTCCAl2gAwIBAgILBAAAAAABFUtaw5QwDQYJKoZIhvcNAQEFBQAwVzELMAkG
…
HMUfpIBvFSDJ3gyICh3WZlXi/EjJKSZp4A==
-----END CERTIFICATE-----
(ellipsis … where data omitted for brevity)
I can view that OK using openssl x509 -in ff.crt -noout -text
(I cut & pasted from Windows to Linux but you can install openssl on Windows too)