ssl_error_rx_record_too_long error on IIS - site was working, suddenly stopped

Question

I am suddenly getting this error connecting to localhost IIS on my development machine. It has been working fine for ages, and now suddenly has this error in Firefox:

Secure Connection Failed An error occurred during a connection to localhost. 
SSL received a record that exceeded the maximum permissible length. 
(Error code: ssl_error_rx_record_too_long)

I have googled and found no clear explanation.

In IE it says:

Internet Explorer cannot display the webpage\

In Chrome it says:

Oops! This link appears to be broken.

Solution 1

This error often happens when Firefox is expecting a SSL connection but instead gets an unencrypted connection. What happens when you follow this link? http://localhost:443/

I've mostly only seen this when the SSL configuration on the webserver was wrong.

Solution 2

I have found the solution and will put it here in case it helps anyone in the future with a similar problem:

The local self signed SSL had expired about 3 weeks ago. For the first 3 weeks it was happy to show the "certificate expired" warning. Today it decided to just die for no apparent reason (when it should still be showing the expired warning).

The solution was to add a new self signed certificate.