First of all get over to: https://addons.mozilla.org/en-US/firefox/addon/2390
Click on the Install button and install the add on into Firefox, restart Firefox and then find the video you want to download. When you are on the page with the video playing click the icon in the status bar at the bottom right of the firefox window and a window will appear. On the window click the Download button and wait for the download to complete. You can then watch the video in your FLV player (if you don't have one, then the plug in recommends FLV Player
You may need to change the file extension of the downloaded file to .flv, to do this right click on the file icon and click Rename, then add ".flv" (without the quotation marks) to the end of the file name.
There are tips provided on the plug in website about how you can convert it to other file formats.
I think that this is a great little plug in for Firefox, it saves me having to keep going to Vixy.net. The perfect plugin for people who want to save on their bandwidth or don't want to search around for ages trying to find that video and best of all it works on all of the following websites:
Youtube, Google Video, iFilm, Metacafe, Dailymotion, Myspace, Angry Alien, AnimeEpisodes.Net, Badjojo, Blastro, Blennus, Blip.tv, Bofunk, Bolt, Break.com, Castpost, CollegeHumor, Current TV, Dachix, Danerd, DailySixer.com, DevilDucky, Double Agent, eVideoShare, EVTV1, FindVideos, Free Video Blog, Grinvi, Grouper, Hiphopdeal, Kontraband, Lulu TV, Midis.biz, Music.com, MusicVideoCodes.info, MySpace Video Code, Newgrounds, NothingToxic, PcPlanets, Pixparty, PlsThx, Putfile, Revver, Sharkle, SmitHappens, StreetFire, That Video Site, TotallyCrap, VideoCodes4U, VideoCodesWorld, VideoCodeZone, vidiLife, Vimeo, vSocial, Yikers, ZippyVideos... and any other webpage with embedded objects.
Not bad really, great find.