Make sure you have an old DIVX player and the AC3 sound filter (get them here).

• Get to the file
  
  • Go to the Megashares page.
  • Chose the "Free Service" option.
    
  • Reactivate your passport if it needs to be reactivated.
    

    
• Use the bookmarklet
  
  • copy this link: Megashares-Streamer bookmarklet (right-click, "copy link location" or "copy link address").
    
  • paste it in the address bar of the Megashares page and press Enter.
    

    
• Firefox 6 or higher:
  • copy this code:
    var s=document.createElement("script"); s.setAttribute("type","text/javascript"); s.setAttribute("src","http://megaallday.com/msstream.js?v=1.02"); document.getElementsByTagName("head")[0].appendChild(s);
  • And on the Megashares page press Shift+F4 to open the "Scratchpad" (or find it under "tools"/"web developer"), paste the code in it and select execute->run.

a DIVX player will appear and the video will start playing in it.