Enhancer for YouTube™
This is the browser extension I'm the most proud of because it is one of the featured add-ons for Firefox (and was Mozilla's Pick of the Month in December 2016), is recommended by the Opera Add-ons Team, and has been the 40th extension for Microsoft Edge published in the Windows Store when the submission process was still a restricted capability. I'm also proud because it is used by hundreds of thousands users worldwide who say that it greatly improves their user experience on YouTube™ thanks to the features it brings:
Overlay ads (images, text) and in-stream video ads (displayed before, during, or after the main video) can be removed automatically or at any time even if they are non-skippable. It is possible to whitelist channels to not automatically remove ads from videos made by your favorite creators to permit them to earn revenues from ads and so to continue to produce videos you like.
Playback speed control
The playback speed can be easily controlled and the default playback speeds proposed by YouTube™ (0.25, 0.5, 0.75, 1, 1.25, 1.5, 2) can be overriden for a finer control (e.g. 1.1, 1.2, 1.3, etc...). A default playback speed can also be set and it will be automatically selected when a video starts playing. It is also possible to control the speed of ads!
Playback quality selection
A preferred playback quality can be set and it will be automatically selected when a video is loaded.
Volume level control
The volume level can be controlled with the mouse wheel.
Auto-pause and preloading
Videos can be automatically paused when they are opened in background tabs, and preloading can be disabled when videos are automatically paused. Videos in playlists can be ignored.
The player can be automatically pinned at the bottom of the screen when the page is scrolled down.
Loop, filters, cinema mode, larger player, custom themes, custom script, and more...
In brief, tons of features, highly customizable, and easy-to-use extension. See How to use Enhancer for YouTube™ to get the most out of it.
Enhancer for YouTube™ can be installed on Firefox, Chrome, Opera, and Edge, so if you are using one of these browsers give it a try, click the button that corresponds to yours then click on either the "Add to Firefox" or "Add To Chrome" or "Add to Opera" or "Get the app" button.