How to save YouTube video from Firefox Cache

In Windows XP:
Open Windows Explorer
Make sure you can see hidden files and folders (Tools > Options > View > Show hidden files and folders)

Go to : "C:\Documents and Settings\xxxxx\Application Data\Mozilla\Firefox\Profiles\xxltouxw.default"
Where xxxxx is your username and xxltouxw is your Firefox profile name

If you cannot see a directory called "Cache" you need to do the following:
Create a text file called "user.js"
Note: This file must be in the same directory as "prefs.js"
Copy the following into the file:

// Path to Cache folder:
user_pref(“browser.cache.disk.parent_directory”,”C:\Documents and Settings\xxxxx\Application Data\Mozilla\Firefox\Profiles\xxltouxw.default”);

Where xxxxx is your username and xxltouxw is the Firefox profile name
Note: It might not be necessary to change xxltouxw if you do not use different Firefox profiles.
Save and close the file "user.js"

If you want to change how much MB Firefox caches, launch Firefox
From the menu select: Tools > Options > Advanced > Network tab page
Enter the amount you want.

OK, watch your YouTube video.
Go back to Windows Explorer
Go to : "C:\Documents and Settings\xxxxx\Application Data\Mozilla\Firefox\Profiles\xxltouxw.default\Cache"
Where xxxxx is your username and xxltouxw is your Firefox profile name
Arrange the files by size (View > Arrange Icons by > Size)
Scroll down to the biggest file.

Copy this file "8DDC0CB5d01" to a directory of your choice.
Rename it to "8DDC0CB5d01.flv"
Note:The filename "8DDC0CB5d01" will be different on your computer.

Now you can play it in your favourite flash player (E.g. Realplayer, Winamp or whatever you use)