On this blog-entry is explained in great detail how to add the Root CA-cerificates to Firefox on a debian based system, like Ubuntu.
{20080504 - \0\UTC\UTCk 18 \pm\5\04 \04\pm\08 124 \2008f \31\02\UTC \08\UTC\pm\Sun, 04 May 2008 14:25:54 +0000 2008}
Install Root CA certificates in firefox
