A great replacement for the old abandoned Youtube Center addon!
It allows to tweak YT and make it more usable.
Works correctly on FF49 x64.

The features I like the most are:
- Remove autoplay up next (so annoying)
- Default video quality
- Grid layout
- Change volume with mouse wheel (even if it's a bit buggy)
- Enable Pop-out mode (but I'd like an exception for the popup blocker)

It misses these good ones from YC, however:
- default player volume (expecially for YT players on external pages)
- show likes\dislikes info on thumbnail (e.g: useful to identify the best videos in a playlist)
- thumbnail preview animation (even if it stopped working a while ago)

Recommended!