Tampermonkey for Chrome

Just open this link.

Click the first step then click "add to chrome" as shown below :

Then It will download a file about 742 KB, after finishing the downloaded file, it will be automatically added to our chrome.

Doneee... For testing it, go to youtube then put these script at the beginning on youtube url :
savefrom.net/ or sfrom.net/, as shown below :

Then press Enter...... Enjoy... Now we can download the vidio... :-)