diff --git a/handshake_server.go b/handshake_server.go
index 823730c..6c40489 100644
--- a/handshake_server.go
+++ b/handshake_server.go
@@ -156,7 +156,11 @@ Curves:
 	if len(hs.clientHello.serverName) > 0 {
 		c.serverName = hs.clientHello.serverName
 	}
-	if hs.clientHello.nextProtoNeg {
+	// Although sending an empty NPN extension is reasonable, Firefox has
+	// had a bug around this. Best to send nothing at all if
+	// config.NextProtos is empty. See
+	// https://code.google.com/p/go/issues/detail?id=5445.
+	if hs.clientHello.nextProtoNeg && len(config.NextProtos) > 0 {
 		hs.hello.nextProtoNeg = true
 		hs.hello.nextProtos = config.NextProtos
 	}