why do you want to download it and it’s already on your machine ?! 
Just go to YouTube or Facebook and watch the video for the first time (make sure it’s all streamed)
Full streamed video from YouTube
DO NOT refresh or close the browser (I tested it with Firefox and Chromium)
then navigate on you Ubuntu machine to the path “/tmp/”, and find the video there named “Flashxxxx” Ta Daaaa
The video on my machine
copy it and rename it to whatever you want and append the extension “.flv”
then you can watch it, or even put it in a folder you wont open again
Watching the video locally
the same thing tested with Facebook videos.
May 29, 2010 @ 07:14:09
Cool
, BTW congratulations for the new theme , i like it much 
May 29, 2010 @ 10:56:11
Thanx, etfaddalo
May 30, 2010 @ 17:59:54
nice
but as I remember this was also in Windows, any fully streamed video is saved automatically in path:
C:\Documents and Settings\\Local Settings\Temporary Internet Files\
but how to find the file? this is what I can’t remember
maybe we can sort icons by date and check the last 2 minutes files
Feb 16, 2011 @ 09:30:58
didn’t work..
Feb 16, 2011 @ 11:47:49
newer versions of flash players on Ubuntu doesn’t save the files there, will check where is it…
Apr 02, 2011 @ 13:33:51
it doesnt work with the new version of Adobe Flash.. bad luck guys.. you can still try your browser’s cache