Comment 4 for bug 696445

What worked for me is installing the identi.ca certificate system-wide:

1. Download it from http://crt.comodoca.com/COMODOHigh-AssuranceSecureServerCA.crt

2. Convert it using this command:

  $ openssl x509 -inform DER -in COMODOHigh-AssuranceSecureServerCA.crt -out outcert.crt -text

3. Copy the resulting file outcert.crt to /usr/share/ca-certificates/COMODO_High_Assurance_Secure_Server_CA.crt

4. Run dpkg-reconfigure:

  $ sudo dpkg-reconfigure ca-certificates

(Details here: http://realmike.org/blog/2011/01/02/ssl-certificate-error-with-gwibber-and-identica-on-ubuntu/)

Not sure whether this is the right fix for the problem, but Gwibber and cURL work after this.