hey guyz, i have found a awesome addon for firefox, its working great on firefox 4 BETA too. this add-on is Sothink Web Video Downloader . it can download all online streaming videos, included famous formats FLV (Flash Video), WMV, ASF, AVI, MOV, RM, RMVB and Flash SWF, supporting YouTube, Google, iFilem and more sites . you can also convert files as you require with the same add-on. to get this add-on , you first required Firefox 3.6 or 4.0 Beta (latest version) you can download this add-on with the following link as XPI for firefox: http://www.sothinkmedia.com/web-video-downloader-firefox/download.htm
I seldom use Firefox. I use Chrome a lot. For video downloader, I think this free YouTube downloader is good. It can download videos from YouTube and other video sites.
There is so many free video downloader add-ons on Firefox, just like Youtube Downloader and NetVideoHunter... I am using both of two.
Speedbit video downloader is also a good option to download any video from any website which can be played by you than it gonna be download by this for sure. It usually comes free with DAP. So worth to try this.