When I open a youtube video with firefox I could not find any video file inside ~/.mozilla/firefox/<some_string>.default/Cache/. I also tried with google-chrome like,

ps ax | grep flash
ls -l /proc/[*PID*]/fd | grep Flash

But again /proc/[*PID*]/fd does not have any video like file. ls -l /proc/[*PID*]/fd have some results like

lrwx------ 1 root root 64 Nov  9 12:18 22 -> /run/shm/.com.google.Chrome.eOsHNu (deleted)
lrwx------ 1 root root 64 Nov  9 12:18 23 -> /run/shm/.com.google.Chrome.p8h6BL (deleted)

Result of ls -l /proc/[*PID*]/fd | grep Flash for some videos from other site is like

lrwx------ 1 root root 64 Nov  9 12:35 26 -> /home/username/.config/google-chrome/Default/Pepper Data/Shockwave Flash/.com.google.Chrome.QMzxP8 (deleted)

But could not be copied.

Then what are the places where firefox or google-chrome stores the streaming videos? And is it possible to recover(copy) a video from there to watch them offline?

P.S

I have other ways(downloaders) to have streaming videos, but my question is very specific.