Thunderbird Certificate Error

Everytime when you send out an email using Thunderbird, and there is an error message telling that there is a Certificate error. To remove this message , please do following:

Step 1: Down the thunderbird "remember_mismatched_domains-1.4.6-fx+tb+sm.xpi" addon
go to http://mirror.internode.on.net/pub/mozilla/addons/2131/

Step 2: In Mozilla Thunderbird, open Add-ons from the Tools menu.

Step 3: Click the Install button, and locate/select the file you downloaded (remember_mismatched_domains-1.4.6-fx+tb+sm.xpi) and click "OK".

Step 4: Restart the mozilla and select "remember the certificate permanently"