As per the title, I upgraded my Mac to Mavericks 10.9.2, and now a bunch of websites which use SSL (aka https) don't work!
What do I do?
Open Keychain Access and delete the DigiCert certificates, but only the ones in the
login keychain - not the ones in
Afterward, you may need to restart your browser and/or network service (switch Airport off and on again, or disable and re-enable Ethernet. If you want to be sure, just restart your computer.
If you're a dummy (like I was) and deleted all the DigiCert entries, you can restore them by manually downloading and installing the 10.9.2 update from Apple.