diff --git a/browser/actors/NetErrorChild.jsm b/browser/actors/NetErrorChild.jsm
index 21354e65f3bd..9aa4ccde2483 100644
--- a/browser/actors/NetErrorChild.jsm
+++ b/browser/actors/NetErrorChild.jsm
@@ -59,6 +59,10 @@ const PREF_SERVICES_SETTINGS_LAST_FETCHED       = "services.settings.last_update
 
 const PREF_SSL_IMPACT_ROOTS = ["security.tls.version.", "security.ssl3."];
 
+let formatter = new Services.intl.DateTimeFormat(undefined, {
+  dateStyle: "long",
+});
+
 function getSerializedSecurityInfo(docShell) {
   let serhelper = Cc["@mozilla.org/network/serialization-helper;1"]
                     .getService(Ci.nsISerializationHelper);
@@ -273,23 +277,25 @@ class NetErrorChild extends ActorChild {
     if (input.data.isNotValidAtThisTime) {
       let nowTime = new Date().getTime() * 1000;
       let msg = "";
+      let notAfterLocalTime = formatter.format(new Date(input.data.validity.notAfterLocalTime));
       if (input.data.validity.notBefore) {
+        let notBeforeLocalTime = formatter.format(new Date(input.data.validity.notBeforeLocalTime));
         if (nowTime > input.data.validity.notAfter) {
           technicalInfo.textContent = "";
-          msg += gPipNSSBundle.formatStringFromName("certErrorExpiredNow2",
-                                                  [hostString], 1);
+          msg += gPipNSSBundle.formatStringFromName("certErrorExpiredNow3",
+                                                  [hostString, notAfterLocalTime], 2);
           msg += "\n";
         } else {
           technicalInfo.textContent = "";
-          msg += gPipNSSBundle.formatStringFromName("certErrorNotYetValidNow2",
-                                                    [hostString], 1);
+          msg += gPipNSSBundle.formatStringFromName("certErrorNotYetValidNow3",
+                                                    [hostString, notBeforeLocalTime], 2);
           msg += "\n";
          }
         } else {
           // If something goes wrong, we assume the cert expired.
           technicalInfo.textContent = "";
-          msg += gPipNSSBundle.formatStringFromName("certErrorExpiredNow2",
-                                                    [hostString], 1);
+          msg += gPipNSSBundle.formatStringFromName("certErrorExpiredNow3",
+                                                    [hostString, notAfterLocalTime], 2);
           msg += "\n";
       }
       technicalInfo.append(msg);
@@ -480,9 +486,6 @@ class NetErrorChild extends ActorChild {
 
         let now = Date.now();
         let certRange = this._getCertValidityRange(docShell);
-        let formatter = new Services.intl.DateTimeFormat(undefined, {
-          dateStyle: "short",
-        });
 
         let approximateDate = now - difference * 1000;
         // If the difference is more than a day, we last fetched the date in the last 5 days,
diff --git a/browser/base/content/test/about/browser_aboutCertError_clockSkew.js b/browser/base/content/test/about/browser_aboutCertError_clockSkew.js
index bb69ba0b440e..5e38cd19605e 100644
--- a/browser/base/content/test/about/browser_aboutCertError_clockSkew.js
+++ b/browser/base/content/test/about/browser_aboutCertError_clockSkew.js
@@ -41,7 +41,7 @@ add_task(async function checkWrongSystemTimeWarning() {
   Services.prefs.setIntPref(PREF_SERVICES_SETTINGS_LAST_FETCHED, Math.floor(Date.now() / 1000));
 
   let formatter = new Services.intl.DateTimeFormat(undefined, {
-    dateStyle: "short",
+    dateStyle: "long",
   });
 
   // For this test, we want to trick Firefox into believing that
diff --git a/security/manager/locales/en-US/chrome/pipnss/pipnss.properties b/security/manager/locales/en-US/chrome/pipnss/pipnss.properties
index 556fc0ca693c..65f5eeaa1e3e 100755
--- a/security/manager/locales/en-US/chrome/pipnss/pipnss.properties
+++ b/security/manager/locales/en-US/chrome/pipnss/pipnss.properties
@@ -285,11 +285,11 @@ certErrorMismatchMultiple3=Websites prove their identity via certificates. %1$S
 
 # LOCALIZATION NOTE (certErrorExpiredNow): Do not translate %1$S (date+time of expired certificate) or %2$S (current date+time)
 certErrorExpiredNow=The certificate expired on %1$S. The current time is %2$S.
-certErrorExpiredNow2=Websites prove their identity via certificates, which are valid for a set time period. The certificate for %S appears to be expired.
+certErrorExpiredNow3=Websites prove their identity via certificates, which are valid for a set time period. The certificate for %1$S expired on %2$S.
 
 # LOCALIZATION NOTE (certErrorNotYetValidNow): Do not translate %1$S (date+time certificate will become valid) or %2$S (current date+time)
 certErrorNotYetValidNow=The certificate will not be valid until %1$S. The current time is %2$S.
-certErrorNotYetValidNow2=Websites prove their identity via certificates, which are valid for a set time period. The certificate for %S appears to be not yet valid.
+certErrorNotYetValidNow3=Websites prove their identity via certificates, which are valid for a set time period. The certificate for %1$S will not be valid until %2$S.
 
 certErrorMitM=Websites prove their identity via certificates, which are issued by certificate authorities.
 # LOCALIZATION NOTE (certErrorMitM2): %S is brandShortName