This is not a very effective method,but its worth a try
Step 1. Use
PMDump to dump your browser memory to your hard disk when you are watching the video you want to rip (you can pause it to avoid the lag)
Step 2. Use a hex editor to open the memory dump file,I use
HxD Editor,its free and portable
Step 3. Press Ctrl + F to search keywords such as "rtmpe://" "mp4:" "stream start" "connect to",there you can find the url you want
rtmpdump 1.9 can successfully download the videos I couldn't download before