How to download a youtube video?
Most addons don’t work with youtube,  there is a possiblity to do that in another way.

Warning!-> Remind that when you use this tool, you leave traces for the webmasters of these tool! 

Step 1: go to Youtube

Step 2: search for the video you want to download and save as MP3 or MP4

Step 3 : change  the url– remove from the word youtube–ube and hit enter

Step 4: choose MP3 or MP4 and select Record.
Now you will see, the video or MP3 will be saved in your dowloadfolder. (Or the one you selected to save your downloads).