Security on the web is impossible, but the attempt here is awareness and education. For those that don't care, nothing will help them. Others however, value information, especially when it can save them from massive headache like identity theft, or getting their bank account cleaned out from being careless online.
This add-on is not hard to use, and the popups, while a nuisance, can be tolerated. If taking a moment to scrutinize a new certificate, or one that has changed for no reason is too much hassle for you, then skip it. Good luck to you.
If however, you realize just how broken the concept of "trust" on the internet is, you will find this add-on a useful tool in gaining a little of that most elusive and valuable commodity, knowledge.
Trust nothing on the internet, not your ISP, especially not your government, nothing. Question everything. Good luck to you, as well.