The cert rotation of Google is annoying me too. I also know the CertPatrol for Firefox, just stopped using it on Palemoon today...But in these days I was annoyed by Googles rotation as well. Looking at the lease time of the certs they even rotate certs with long time validity. My first idea was they have some load sharing to different worker servers and one day I have all certs accepted, but no, they are really rotating all the time.
I still think, watching the certs is a good thing as I'm sometimes on untrusted networks and most of my email servers don't rotate that often. If you have that option to ignore cert changes in Aquamail, please make it an account option and not a global one.