I think you have deleted your old add-on and replaced it with this one? The issue with this new add-on that it makes trouble to work with Firefox portable, the old one was installing the ffmpeg.exe in the user's profile, but now it's going to be installed on this path C:\Users\(username)\AppData\Roaming\ffmpeg.exe

Still impressive...
But now mp3 convertion has problem and automation used to be easier.
How add some buttons for FF not in the YT panel. Like download video, dl video AND audio, download just the mp3, because i usually use in two ways and just one default option isn't good for me.
Also, i can't teach to my granpa the difference between aac, opue ogg... i want to set some default value and the only choice for him should be mp3 or video. If granpa can use it, everyone can.

Love it for downloading music from youtube videos.

Best downloader so far ! No new tab ! Just select what and how you want, and downloads straight away and even in high quality ! Congratulations !

Awesome