YouTube Enhancer Plus Alternatives

YouTube Enhancer Plus

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Warning: YouTube Enhancer Plus does not support the Material Design version of YouTube, and since Mozilla has planned to disable XUL add-ons like this one when Firefox 57 will be released (source) I have decided to stop its development, so I highly recommend you to use Enhancer for YouTube™ instead.
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YouTube Enhancer Plus will greatly improve your YouTube experience! It allows you to disable autoplay for videos loaded in background tabs, remove ads from videos (automatically or on-demand), remove annotations, automatically play videos in HD or any other preferred format, play videos in cinema mode for a comfortable and distraction-free watching, resize the video player, automatically repeat videos, change YouTube's style using custom themes, save your favorite videos and playlists to watch them in the built-in Firefox sidebar while doing something else such as surfing the web, and more...