way 1
Play the video file
After streaming open computer > filesystem > temp
Copy the video file and paste in some folder and rename it
(don't close the web broser before copying the file)
way 2
Open web browser
Click on bookmarks > get bookmark addons
Select dowload management from categories
Click on video download helper
download and install
restart mozilla
when you play a video from a website the download helper will roll(near the address bar)
Click on the arrow near to it and download the video