The first way :
select the video you want to download, play the video until it is finished, do not close your browser. Search / tmp in the Filesystem. There is a file extension. flash and then copy the files. flash. After that play video on your favorite video player.

The second way :
install youtube-dl application with the following syntax:

sudo apt-get install youtube-dl

then copy the url of the video that you select in syntak following :

youtube-dl [url-video-in-youtube]

Good luck !!!

source : http://opensource.telkomspeedy.com/wiki/index.php/Cara_mudah_download_video_dari_youtube_di_Ubuntu

A simple way to block porn sites using the Firefox browser.

•     Install Firefox.
•     click Tools -> Add Ons.
•     Enter the keyword "Parental Control"
•     Select Add ons that you like
•     Click the "Add to Firefox"

Following recommendations from various sources for the Add-Ons that say simply and effectively used to block sites that are not good

• FoxFilter - Recently called "THE Parental Control for Firefox"! FoxFilter is a personal content filter that helps block pornographic and other inappropriate content. All filtering features are free! Premium features available with small support fee. 

Website : http://www.inspiredeffect.com/FoxFilter

• BlockSite - BlockSite is an extension, which automagically blocks websites of your choice. Additionally, this extension will disable all hyperlinks to these websites, by just displaying the link text without the clicking functionality

Website  : https://addons.mozilla.org/en-US/firefox/user/32208

Good Luck !!!