Have you ever had that issue where a volume booster add-on would just forget what volume did you set it to on a page, or would outright mute some pages? No? Well, I have, and it's quite frustrating. That's why I created this add-on.
This is a simple free & open-source add-on that allows you to boost the volume of any* page and will (thankfully) remember the volume you set it to.
*Its only (known) limitation is that it can't boost the volume of webpages which play DRM-protected content using JavaScript, such as Netflix and Spotify.
It has two sliders: a global one and a domain-specific one. You can delete the domain-specific volume multiplier by clicking the trash can icon next to the slider. In that case, the global one will be used.
Clicking the note button will set the sound mode to either mono (♪) or stereo (♫). The default is stereo.
You can also go to the add-on's option page to change the hard volume boost limit to any value between 100% and 1000% (as well as other stuff). This is useful if you want to prevent yourself from accidentally setting the volume to a very high value and consequently blowing your ears off. The default is 500%.
I am not responsible for any damage to your ears or headphones that may result from the add-on use. Use the add-on responsibly and ensure your headphones can handle the boosted volume levels.
Available on the Firefox Add-ons site (AMO)
or directly on this GitHub repository's releases page.
You can see the changes made in each version in the CHANGELOG.md file.