--- a/browser/base/content/pageinfo/security.js
+++ b/browser/base/content/pageinfo/security.js
@@ -85,16 +85,19 @@ var security = {
           retval.version = "TLS 1.0";
           break;
         case nsISSLStatus.TLS_VERSION_1_1:
           retval.version = "TLS 1.1";
           break;
         case nsISSLStatus.TLS_VERSION_1_2:
           retval.version = "TLS 1.2"
           break;
+        case nsISSLStatus.TLS_VERSION_1_3:
+          retval.version = "TLS 1.3"
+          break;
       }
 
       return retval;
     } else {
       return {
         hostName : hostName,
         cAName : "",
         encryptionAlgorithm : "",

--- a/devtools/shared/webconsole/network-helper.js
+++ b/devtools/shared/webconsole/network-helper.js
@@ -716,16 +716,18 @@ var NetworkHelper = {
   formatSecurityProtocol: function(version) {
     switch (version) {
       case Ci.nsISSLStatus.TLS_VERSION_1:
         return "TLSv1";
       case Ci.nsISSLStatus.TLS_VERSION_1_1:
         return "TLSv1.1";
       case Ci.nsISSLStatus.TLS_VERSION_1_2:
         return "TLSv1.2";
+      case Ci.nsISSLStatus.TLS_VERSION_1_3:
+        return "TLSv1.3";
       default:
         DevToolsUtils.reportException("NetworkHelper.formatSecurityProtocol",
           "protocolVersion " + version + " is unknown.");
         return "Unknown";
     }
   },
 
   /**

--- a/security/manager/ssl/nsISSLStatus.idl
+++ b/security/manager/ssl/nsISSLStatus.idl
@@ -15,16 +15,17 @@ interface nsISSLStatus : nsISupports {
   readonly attribute ACString cipherName;
   readonly attribute unsigned long keyLength;
   readonly attribute unsigned long secretKeyLength;
 
   const short SSL_VERSION_3   = 0;
   const short TLS_VERSION_1   = 1;
   const short TLS_VERSION_1_1 = 2;
   const short TLS_VERSION_1_2 = 3;
+  const short TLS_VERSION_1_3 = 4;
   readonly attribute unsigned short protocolVersion;
 
   readonly attribute boolean isDomainMismatch;
   readonly attribute boolean isNotValidAtThisTime;
 
   /* Note: To distinguish between
    *         "unstrusted because missing or untrusted issuer"
    *       and