Volume Scroll lets you control your main volume by hovering with your mouse cursor over the top menubar and scrolling up or down to change your volume.
SoundFixer Alternatives
SoundFixer is described as 'Helps you fix annoying sound problems on sites like YouTube: audio in one channel only, too quiet or too loud' and is an app in the web browsers category. There are more than 25 alternatives to SoundFixer for a variety of platforms, including Windows, Linux, Mac, Google Chrome and Flathub apps. The best SoundFixer alternative is EarTrumpet, which is both free and Open Source. Other great apps like SoundFixer are FineTune, Volume2, Browser Boost and Background Music.