There are a number of add-ons which you can install to download youtube videos, but I don't recognize the one you described. You'd have to ask your friend what the name of it is.

However, here's one that does a similar job: https://addons.mozilla.org/en-US/firefox/addon/flash-video-downloader-youtube/

In the screenshot, you can see a blue arrow on the toolbar. If you click that, you get the option of downloading that particular video in a number or diferent formats like High Definition (HD) for example.

If the arrow remains greyed out on a video, it means that downloading has been disabled by the site.

Thank you a lot , i understand every word you just said! I downloaded the add-on and went straight onto a youtube video but this message comes up when i double click on the download...

There is no default application specified to open the document flash_video_downloader_youtube_downloader-2.0.21-fx.xpi.

Thank you again

After you installed the add-on, did you checkmark the box which asks you to accept the terms before continuing?

Sorry i don't know what you mean by checkmark, we might be from different countries and i may use a different word but nothing actually came up about accepting the terms!

checkmark = tick in the box

Try this one instead: https://addons.mozilla.org/en-US/firefox/addon/download-flash-and-video/

Thank you so much, you have been a excellent help! I think i know what i was doing wrong, i would download the add-on but wouldn't actually add it to my firefox. I have downloaded the last link you have sent me and it lead me to another page, so i have started to download that and it shouldn't take too long now! I will get back to you asap. THANKYOU :)

Once you've downloaded a flash video, you'll still need a player to view it. Apple has a freebie one you can download @ http://www.apple.com/downloads/macosx/video/swfflvplayer.html

All is working. Thanks :)

You're welcome.

Could you please click the "Solved it" button to take your post out of the loop?

Thanks.

Sure :)