mkVolumePerTab od mkultra

mkVolumePerTab lets you control the volume of HTML audio and video independently for each Firefox tab.

Open the extension popup to adjust the current tab’s volume from 0% to 100%, mute or unmute media, and optionally save a volume preset for the current website.

The first release is designed primarily for controlling voice and video messages in WhatsApp Web, but it also works with standard HTML <audio> and <video> elements on other websites after you grant access to the current site.

Features
Independent volume level for each tab
Volume range from 0% to 100%
Mute and unmute controls
Saved volume presets by website
Support for media added dynamically after the page loads
Automatic handling of site-initiated volume changes
Optional access to additional websites
Restoration of original media volume when control is disabled
Light and dark interface
No analytics, tracking, remote scripts, or external services
Limitations

mkVolumePerTab controls standard HTML media elements only. It does not control the operating system mixer, microphone volume, WebRTC calls, DRM-protected content, Firefox system pages, or audio created exclusively through the Web Audio API. Audio amplification above 100% is not supported.