How to download youtube video without any software

Many people download their fav youtube videos either by using a software or going into certain sites like savetube  and paste their links.Now am going to tell you a trick which requires no third party software or no other  site to download youtube videos.You can download youtube videos using ur mozilla or chrome browser.
Add a bookmark in your chrome or firefox and save this following code .
To download video in FLV  format
  javascript:window.location.href = 'http://youtube.com/get_video?video_id=' + swfArgs['video_id'] + "&l=" + swfArgs['l'] + "&sk=" + swfArgs['sk'] + '&t=' + swfArgs['t'];
To download video in MP4 format
javascript:window.location.href = 'http://youtube.com/get_video?video_id=' + swfArgs['video_id'] + "&fmt=18" + "&l=" + swfArgs['l'] + "&sk=" + swfArgs['sk'] + '&t=' + swfArgs['t'];