I am seeingWe suspect that the problem involves the Firefox browser, possibly following the latest update."This Connection Is Untrusted" - You have asked Firefox to connect securely to 7749195048983246407_73be54cd6d1c58526e719a5edd6d94a945570409.blogspot.com, but we can't confirm that your connection is secure.This prevents me from using various preview features.
We have a new Problem Rollup topic, in Blogger Help Forum: Get Help with an Issue, where we are requesting details from everybody who is experiencing this problem.
Right now, the problem appears to involve Firefox V36, and attempts to use Live Preview (Template Designer), Post Preview, and Template Preview (Template Editor), when updating blogs published to custom domains. The simplest solution, in this case, may be to un install V36.
(Update 3/6): Mozilla may have fixed this, in V36.0.1.