CA certificates aren't really updated all that often. For Windows and Internet Explorer they generally come in as part of Windows update.
If you are running your own Certificate Authority or if you want to trust a certificate authority not blessed (eg cacert.org) by Microsoft you usually would do this by setting up a group policy to distribute the CA certificate.
As far as I am aware there isn't really a good way to distribute CA certificates in a way that will be useful for alternate browsers like Firefox. For alternate browsers you usually get updates when you update the browser.