No documentation on how to set it up and get FFMPEG working. The support site is just a GitHub page with nothing on it but some files, not even a release.

Downloads audio-only when I select movie+audio

It is broken. Youtube has changed something to the effect that the video file extensions and the audio file extensions are switched.
The workaround (manually renaming the files as they are saved to disk) is kind of a pain in the ass.

Also, switching the "Homepage" from:
https://github.com/inbasic/iaextractor/
to:
https://addons.mozilla.org/en-US/firefox/addon/youtube_downloader_webx/
would be very nice.

virus un .bat comme d'hab ( j'ai même pas télécharger l'extension ptdr(plié tordu de rire) tas de merde !

holly freaking crap, why did you have to destroy one of the only reason I use firefox for?
where is the short cut download? why can't I chose a default download location? why is there no "quick" download option...

At least with the old version you could set it as a one click download if you didn't fancy the shortcut... but here the quick download means that I have to locate the icon, click, click "quick" download (wow that's real quick... one click faster then selecting the quality).

I used to just have YouTube run in the background and if there was a song I'd like I'd quickly switch and press CTRL+SHIFT+D.
I get that things needs to be updated and all, but are developers just oblivious to the users?

I'm already mad that Firefox forces those dumb "highlights" as if I didn't know what I'm looking at (granted I can disable them, but not enable more then two rows of most visited?!?!?!)

I've managed to get around the custom folder problem by first selecting the default location for firefox, then just setting firefox to "always ask" (something that I prefer anyway), still the actual quick download (one click) would be nice and shortcut would make this a five star add-on!

Tried this on two pcs (same os & FF version). One works fine, the other downloads the two streams but is then unable to find the downloaded streams! Rechecked the limited settings, reinstalled .. zilch. Only other difference - on the one that works I got a firewall exception request which I allowed. No alert on the other one. Suggestions anyone???? Short of manually merging the streams using ffmpeg.
The support page has several posts but no replies from the author.