Rated 2 out of 5 stars

This was the only free (not freemium) and complete (all resolutions) downloader for Youtube but:
- on Firefox 52 ESR, the latest 2 versions stopped working (unclickable menu).
- lately, v5.7.31 causes some heavy memory leak on Youtube that hangs the browser.
- the dev wanted to completely rewrite the addon as a webextension, but there are no news since months. And the email address seems deactivated. This extension has probably been abandoned. :(

Rated 4 out of 5 stars

The only free addon that lets you easily save full (non-protected) videos from Youtube (even Dash formats).
It's also quickly updated after each YT change.

The current version (5.7.36), however, has still some problems:
sometimes the download fails without warning or the program doesn't mux the audio.

Example to manually join video+audio via command line:
ffmpeg.exe -i "video.mp4" -i "audio.m4a" -vcodec copy -acodec copy "1output.mp4"

This review is for a previous version of the add-on (5.7.34).