Update...

Alright... in my further retarded-ness I seem to have actually uploaded the wrong firefox extension. That was a former extension that allowed you download youtube videos as flv files.

I recommend re-installing the firefox extension (I have linked the correct one now) and installing it because it's the one that actually works with this program
(you can uninstall the other one, or keep it maybe you need raw flv video for something? Oo)

also
I have made the extension for opera and I have tested it. It appears to work fine for me.

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writing the opera extension was actually easier than writing the firefox extension.