To install Adobe Flash Player in Kali Linux is very easy.
1. Download Adobe Flash Player .tar.gz from http://get.adobe.com/flashplayer/.
2. Using Terminal, extract the content by issuing this command:
tar zxvf adobe_flash_player_filename_here.tar.gz
3. Copy the ‘libflashplayer.so’ file and paste it into Mozilla plugins folder.
cp libflashplayer.so /usr/lib/mozilla/plugins/
4. That’s it! Now you can watch Youtube video without problem.
If you stuck with errors, Kali has a community forum that you can ask and request for helps. Feel free to drop by and say hi at the forum.