--- a/security/manager/ssl/nsNSSIOLayer.cpp
+++ b/security/manager/ssl/nsNSSIOLayer.cpp
@@ -70,17 +70,17 @@ namespace {
 // does not impact other normal sockets not using the flags.)
 //
 // Their current definitions are:
 //
 // bits 0-2 (mask 0x07) specify the max tls version
 //          0 means no override 1->4 are 1.0, 1.1, 1.2, 1.3, 4->7 unused
 // bits 3-5 (mask 0x38) specify the tls fallback limit
 //          0 means no override, values 1->4 match prefs
-// bit    6 (mask 0x40) specifies use of TLS 1.3 compatibility mode (draft-22)
+// bit    6 (mask 0x40) was used to specify compat mode. Temporarily reserved.
 
 enum {
   kTLSProviderFlagMaxVersion10   = 0x01,
   kTLSProviderFlagMaxVersion11   = 0x02,
   kTLSProviderFlagMaxVersion12   = 0x03,
   kTLSProviderFlagMaxVersion13   = 0x04,
 };
 
@@ -89,21 +89,16 @@ static uint32_t getTLSProviderFlagMaxVer
   return (flags & 0x07);
 }
 
 static uint32_t getTLSProviderFlagFallbackLimit(uint32_t flags)
 {
   return (flags & 0x38) >> 3;
 }
 
-static bool getTLSProviderFlagCompatMode(uint32_t flags)
-{
-  return (flags & 0x40);
-}
-
 #define MAX_ALPN_LENGTH 255
 
 void
 getSiteKey(const nsACString& hostName, uint16_t port,
            /*out*/ nsACString& key)
 {
   key = hostName;
   key.AppendASCII(":");
@@ -2575,16 +2570,22 @@ nsSSLIOLayerSetOptions(PRFileDesc* fd, b
     }
   }
 
   SSLVersionRange range;
   if (SSL_VersionRangeGet(fd, &range) != SECSuccess) {
     return NS_ERROR_FAILURE;
   }
 
+  // Set TLS 1.3 compat mode.
+  if (SECSuccess != SSL_OptionSet(fd, SSL_ENABLE_TLS13_COMPAT_MODE, PR_TRUE)) {
+    MOZ_LOG(gPIPNSSLog, LogLevel::Error,
+            ("[%p] nsSSLIOLayerSetOptions: Setting compat mode failed\n", fd));
+  }
+
   // setting TLS max version
   uint32_t versionFlags =
     getTLSProviderFlagMaxVersion(infoObject->GetProviderTlsFlags());
   if (versionFlags) {
     MOZ_LOG(gPIPNSSLog, LogLevel::Debug,
             ("[%p] nsSSLIOLayerSetOptions: version flags %d\n", fd, versionFlags));
     if (versionFlags == kTLSProviderFlagMaxVersion10) {
       range.max = SSL_LIBRARY_VERSION_TLS_1_0;
@@ -2596,27 +2597,16 @@ nsSSLIOLayerSetOptions(PRFileDesc* fd, b
       range.max = SSL_LIBRARY_VERSION_TLS_1_3;
     } else {
       MOZ_LOG(gPIPNSSLog, LogLevel::Error,
               ("[%p] nsSSLIOLayerSetOptions: unknown version flags %d\n",
                fd, versionFlags));
     }
   }
 
-  // enabling alternative handshake
-  if (getTLSProviderFlagCompatMode(infoObject->GetProviderTlsFlags())) {
-    MOZ_LOG(gPIPNSSLog, LogLevel::Debug,
-            ("[%p] nsSSLIOLayerSetOptions: Use Compatible Handshake\n", fd));
-    if (SECSuccess != SSL_OptionSet(fd, SSL_ENABLE_TLS13_COMPAT_MODE, PR_TRUE)) {
-          MOZ_LOG(gPIPNSSLog, LogLevel::Error,
-                  ("[%p] nsSSLIOLayerSetOptions: Setting compat mode failed\n", fd));
-          // continue on default path
-    }
-  }
-
   if ((infoObject->GetProviderFlags() & nsISocketProvider::BE_CONSERVATIVE) &&
       (range.max > SSL_LIBRARY_VERSION_TLS_1_2)) {
     MOZ_LOG(gPIPNSSLog, LogLevel::Debug,
             ("[%p] nsSSLIOLayerSetOptions: range.max limited to 1.2 due to BE_CONSERVATIVE flag\n",
              fd));
     range.max = SSL_LIBRARY_VERSION_TLS_1_2;
   }