Yahoo mail is inaccessible from Firefox, because of it’s invalid/expired security certificate.

Very nice, yahoo, keep up this path and you’ll end up with a worse version of your mail service then you had 10 years ago…. Oh, wait, it’s already worse !

Yahoo mail's security certificate is expired
Yahoo mail’s security certificate is expired


(Click on the image for a higher resolution)

Screenshot was taken on Saturday, January 10, 2015, the time is visible in the screenshot