I had to stop using it because in every case, no matter what settings I set, the keyboard controls stopped working after watching a video for a while. Specifically the spacebar. When I first loaded a video on youtube and started fullscreen playback the spacebar worked as normal. Press it once to pause press it again to resume. But after a fairly short time (Maybe 15 minutes) of video playback pressing the spacebar will only pause the video while you hold it down. As soon as you let off the spacebar playback resumes. If you hold it down long enough it will start switching rapidly between pause and resume, but in all cases playback resumes as soon as you let off the spacebar. So it becomes impossible to pause the video playback with the spacebar, you have to use the mouse, which is extremely irritating as I use a wireless keyboard to control playback when not sitting at my computer. Using the mouse in this situation is not acceptable. I have observed this behavior on Windows 10 Build 1809 and on Ubuntu Linux 18.10. On Firefox 64.02 and 65 beta. As soon as I remove the extension, the problem goes away. It's a shame because I really enjoyed most of the other features.

i turn off popup window and if i play yt films and click on backwards on page then popup is show https://i.imgur.com/14jOdoV.png

Please Update - YT changed something - Vidoes stopped loading!
After one Month Developer not changed anything - Useless.

Iridium for YouTube has been seemingly completely wiped. The functionality of it is gone and going into the settings reveals that everything says "coming soon"
wouldn't it make sense to keep the old version working until the new version is done?

Перестало воспроизводить видео
Прошел целый ГОД! А оно все равно не работает на FF! Было раньше хорошее приложение, а теперь только название. Дофига функций из которых только работает смена фона. Периодически полгода-год ставлю в надежде что исправили проблему. Но видимо всем пофиг.
Повторю проблему: ставлю этот аддон, включаю любое видео, и либо крутится кружок бесконечно, либо стоит превью картинка и нельзя нажать в центре логотип ютуба.
Прошло ещё 2 года с предыдущего отзыва:
Не работает с включенным Adblock (getadblock)

It breaks YouTube. YouTube won't play.

I used to give a 5 star review, unfortunately I have to amend that decision until a certain feature is re-implemented. I really like the new interface and design of Iridium and the dark theme is cool. But the one single feature that I use this for above all else is gone now, control volume with scroll wheel when cursor is in the video window.

I've read the github post and understand the creator is frustrated. I've been with this addon for like five years now and have been through all of the ups and downs, the YouTube system completely changing and breaking everything, I feel ya. For now I'm reverting to an old version that still has some functionality for me. The mouse wheel volume control has always been the most reliable feature imo. Literally every other function could completely stop working, but the volume control continued, and that's all I really cared about. Hopefully when the new version has the features re-implemented, I will update and go back to a solid 5 star review. Please focus on mouse wheel volume control and reverse playlist control. That's all it needs for a 5 star from me.