Download YouTube Videos:
Open your Firefox browser.
In the upper left-hand corner click on the orange “Firefox” tab, then “Add-ons”
In the upper right hand corner, type “youtube” in the search box.
Find the “YouTube Video and Audio Downloader 0.3.9.1” (about 5th down in list) and click “Install”
After installing restart your browser. A YouTube logo will appear in the upper right hand corner. Click on the logo, to make an orange box appear with your new options. Clicking on “Quick Download” while on the page of the video you wish to download, will download that video.