Here! For this reson we have very nice extension compatible with firefox. The usage of extension is quite easy.
For using this extension, you should have the firefox installed in your computer. You can download the firefox from the next side.
Also you can download both the extension from here.The name of the extension is Video DownloadHelper.
Now, if we downloaded the firefox, let’s to go on to the setup of extension.
After you clicked for downloading the extension, such screen will appear.

We are waiting for seconds to expire and now we are clicking to setup.
After setting up, we are restarting the firefox and our extension is ready for usage.
Now, let’s to test at the youtube on a video.
Open a video which you want to watch. Click the right button on a blank space at the page.

Choose the video from below and download.
There is at this address a known list of sites in which extension can download video. Also at the end of the article i add both some addresses. You can add unexistences in these addresses and video sites in which extension works with Submit a new site.
Some sites in which you can download video:
1. http://www.youtube.com/
2. http://video.google.com/
3. http://quicksilverscreen.com/
4. http://izlesene.com/
5. http://www.dancehallreggae.com/
6. http://www.livevideo.com/
7. http://realclips.net/
8. http://www.videocopilot.net/
9. http://videogalaxy.tv/
10. http://youporn.com/
11. http://redtube.com/
12. http://xvideos.com/
13. ...
14. ...
Let’s mention about the extension a little.
Tools>Extensions

A window will be open like following. Window which shows extensions.

We are clicking Options from here.
Such window will appear.

From here you can choose format and location where you want to download videos.
At the time of using the extension you can be informed from new video sites which are continuously being added. There can be hundereds of video sites which are not known by you.

For arriving at the position which is at the upper picture, we are clicking the right at the page in which is video. We are clicking the supported sites. A window will appear like following.

As you see you can download with this extension from hundereds of video sites. Your unique necessity is the Firefox and DownloadHelper extension.
At these sites there is both numbers of video sites whose content is leaning against adults. You can download video with this extension at the whole of video sites to occur to you.