Many people have been asking how to download youtube videos, and kept being pointed to useless software which will do it for them.
Here is the easy way:
Step 1: Find the video you want to download and wait for it to completely finish loading.
Step 2: Minimize your browser (do NOT close it, some browsers delete the temp directory upon closing), and navigate to the directory /tmp
Step 3: Drag the flash file onto your desktop. Voila!
This definitely works with firefox, and probably most other browsers aswell. Enjoy!