buffering location /tmp? I was a long time Ubuntu user before I moved on to a Mac; so I'm used to seeing videos on YouTube and copying the buffered files from /tmp to another place for later viewing, if I like the video.

I tried doing the same on my Mac but its not working. Are the videos being buffered to a location other than /tmp?
Likely they reside in the Application's Cache directory.

Look into (HOME)/Library/Caches and (HOME)/Library/Application Support