Rated 4 out of 5 stars

I love the idea of notifying users when certificates change, but is it really important to show certificate details the first time when I visit an https site? If you really feel it is vital, I would encourage you to make it a preference value (enabled by default).
Otherwise, good idea and good job. Thanks!

This review is for a previous version of the add-on (0.7). 

It's in 1.4

We've had it in the 1.3beta series for a while, now it is public with version 1.4: New certificates do not pop up by default any longer, and there is a preference switch to change that.