--- a/dom/media/webvtt/vtt.jsm
+++ b/dom/media/webvtt/vtt.jsm
@@ -1433,17 +1433,17 @@ this.EXPORTED_SYMBOLS = ["WebVTT"];
         if (self.state === "HEADER") {
           line = parseHeader();
         }
 
         while (self.buffer) {
           if (!line) {
             // Since the data receiving is async, we need to wait until the
             // buffer gets the full line.
-            if (!/\r\n|\n/.test(self.buffer)) {
+            if (!/\r\n|\n|\r/.test(self.buffer)) {
               return this;
             }
             line = collectNextLine();
           }
 
           switch (self.state) {
           case "ID":
             // Ignore NOTE and line terminator