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WebExtension that shows certificate chains in an aesthetically pleasing manner.
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Certainly Something (Certificate Viewer)

Uses the new TLS Info API in Firefox to view information about the current state of your HTTPS connection.

Main Info Extensions

It currently requires at least Firefox 62.

Developing and Installing Locally

It is recommend that developers use web-ext for installation and testing. It provides a number of useful features, such as automated installation and autoreload upon source changes.

Install web-ext using the following command:

$ npm install --global web-ext

For testing and development, run the following commands in two separate terminal windows:

$ npm run-script watch
$ web-ext run --browser-console -s build --start-url ''

If you are simply looking to give it a single run, you can compile it by running:

$ npm install
$ npm run-script compile

And then in Firefox, go to -> Add-ons -> Extensions -> (Gear Icon) -> Debug Add-ons -> Load Temporary Add-on

Navigate to build/manifest.json and it should start running immediately.

Supported Functionality

  • Handshake information (TLS version, cipher suite, signature scheme)
  • Subject and issuer information (common name, organization, etc.)
  • Validity date ranges
  • Subject alternative names
  • Subject public key information (SPKI)
  • Certificate downloading
  • Key usage
  • Serial numbers
  • Fingerprints
  • Extensions, including
    • Basic constraints
    • Extended key usage
    • Certificate revocation list (CRL) endpoints
    • Authority information access (AIA)
    • Certificate policies (most common policies)
    • Subject key identifiers
    • Authority key identifiers
    • OCSP stapling
    • Embedded SCTs, including CT log names


Thanks so much to Ryan Hurst and Yury Strozhevsky for doing the painful work in PKI.js and ASN1.js, without which this project could not have been accomplished.

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