I also have the Video Download Helper extension with the local helper app installed. This add-on succeeded on youtube when that one failed. I will likely keep it and just have it disabled until I need it, but it seems to work.

EDIT: Disabling it makes it clutter up the youtube page even more. The button spot turns into a bunch of html links to the videos. 4 Stars for it working when others failed, -1 star for it not fully disabling. I ended up removing it as it seems to be sketchy at this point.