Quote:SoundFixer is an extension for the Firefox web browser that attempts to fix sound related issues on YouTube and select other sites with audio.

Internet users who watch videos with audio on the Internet may run into a number of issues: audio may be too quiet or too loud, or sound output uses a single channel only.

While you can adjust the volume of sound using built-in volume controls, volume options of the operating system, and maybe even volume options of the speakers or headphones that you are using, it is sometimes the case that these don't fix the issue at all that you experience or that it is too cumbersome to use these controls regularly.

Full reading: https://www.ghacks.net/2018/11/02/soundfixer-fixes-sound-issues-on-youtube/