The video at https://www.youtube.com/watch?v=VVjMP2DPDBo works in the browser, but only when signed in, otherwise it displays a screen that says "Content Warning The video you have requested has not been rated and may contain content intended for mature audiences. <...> Sign in to confirm your age".

The YouTube plugin has no "Sign-in" functionality, so attempts to download with FRD 0.9u4 end with "ERROR - SWF URL not found". The log for this link is attached.

Thanks for the report.

Please try plugin v2.9.6. The "sign-in" functionality is still not supported.

Wow, that's fast Seems to work now, thank you kindly.