I have a proxy server that runs on my local system. It's designed to capture traffic that passes through it for testing. It generates a self signed certificate that it uses to sign traffic.

Here's how it's explained from the documentation:

If your application uses SSL (HTTPS), the proxy must act as a man-in-the-middle to record traffic. To do this the proxy server must have a root certificate that it can use to sign its communication with the app. By default, the proxy server generates a unique root certificate, and no user intervention is needed. However, when browsing the app you will get SSL warnings.

My question is that some sites allow me to add an exception and others don't.

For example duckduckgo and google don't give me the option but imgur does. This happens when using the proxy with Chrome and Firefox.

I'm not too concerned about google but I have some internal sites I am working with so I am trying to figure out what might be causing this.


  • 2
    If the site uses HSTS you can't add an exception
    – paj28
    Commented Aug 17, 2018 at 14:55
  • Thanks @paj28 I noticed that in the error shortly after posting.
    – kweinert
    Commented Aug 17, 2018 at 15:44

1 Answer 1


I think I figured it out after posting. It pays to pay attention to the errors I guess.

Firefox says

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate.

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