Can Firefox add-ons access information in the SSL/TLS handshake?

I’ve been searching through the API documentation all day, but haven’t been able to find anything that gives access to information contained in the SSL/TLS handshake (such as the modulus value provided by the server). Everything I can see is for accessing the HTTP headers after the handshake is already completed.

Is this possible to do with add-ons in Firefox? I realize I can get the modulus prime value by querying the server with OpenSSL in a separate request, but I want to see which prime value the Firefox HTTPS requests are receiving each time requests are made.


That sounds like it’s too low-level to be exposed by any XPCOM API.

I came across an addon that mentioned TLS, you might find this interesting, although not really an answer to your topic:

That’s what I was worried about … I’m thinking the only option would be to watch the traffic from outside of Firefox and pipe the info into the plugin somehow.

Do you know of any other option to pull this off from within Firefox, without needing to write external software?

Nothing comes to mind.

More about custom TLS (not necessarily HTTPS):
Can we make a TLS connection with different verification settings without affecting global settings?

  • Possible case 1: Ignore any verification errors for a certain connection (because no authenticity is assumed)
  • Possible case 2: Require the server certificate to match a certain fingerprint for a connection. But it is not in the trust store (nor should it be)
  • Possible case 3: Require the server certificate to be signed with a certain certificate for a connection. But it is not necessarily in the trust store.

Also, can we get the server certificate from a TLS connection? It may not be for HTTPS. We sometimes want to use raw connections, especially to implement TLS’d protocols. What API can we use? Of course, WebSockets are not always usable. We’re tired of binary components or js-ctypes.
hint: we’re planning a new add-on – it will be amazing, I promise!


  • HTTPS Everywhere seems to use js-ctypes just for SSL Observatory.

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