good

It doesn't work. No Download button ever appeared. Tried a number of Youtube clips and rebooted.

The button never shown on sidebar.
(Firefox 70.0.1, Windows 10 1809)

Can only download 720p it seems but it's also the only add-on I've found that works as intended.

Works, HD formats too.

It works and will download videos, but it will only download the AVC (MP4) version of videos. For example, YouTube primarily uses VP9 and Opus codecs for their higher quality streams now, but this will not download those versions and will instead download H.264 and AAC versions, meaning they are lower quality as a result. So while it works and downloads YouTube videos, it will not be pulling in the best possible stream despite having selected the resolution I wanted in the video player first.

It work and i recommend it.

Very fast because it's not using a 3rd party converter/download service but you directly pull the video from YT as fast as your internet connection allows you to.
The download button sometimes takes a hot second to appear, which would be a nice fix.

Gave it another try and it indeed working now. Before the download button would not appear. But now it appears and it downloads videos. Changing my review to reflect that it works now.

there is no download button under the video players.