you can get the right extension here http://javimoya.com/blog/youtube_en.php once you downloaded it, you will see an icon at the bottom right of your firefox browser. click on it the next time your watching youtube or any other site like Yahoo! Videos to download while-you-watch. The renaming should be done in the desktop just to be safe coz i haven't tried downloading it directly to one of my folders. And the renaming should be done immediately after downloading coz i had this prob when you don't do it in a while, you won't be able to change it. Hope you'll be successful!