Try downloading another copy of Firefox and run it from the folder. Do not sign into your Firefox account and see if you have the same issue.

https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

What desktop are you running? I also see the same thing with each tab being at 100% volume. see screenshot Firefox or Desktop Environment issue... I would guess Desktop, but someone more websavvy will have to chime in.

Operating System: openSUSE Tumbleweed 20211228 KDE Plasma Version: 5.23.4 KDE Frameworks Version: 5.89.0 Qt Version: 5.15.2 Kernel Version: 5.15.8-1-default (64-bit) Graphics Platform: X11 Processors: 4 × Intel® Core™ i7-4810MQ CPU @ 2.80GHz Memory: 31.0 GiB of RAM Graphics Processor: Mesa DRI Intel® HD Graphics 4600

Thanks for the reply! Unfortunately downloading and running from the folder did not solve my problem - although I'm kind of glad to see the same happening on someone else's machine :)

This is my environment

OS: Fedora release 34 (Thirty Four) x86_64 Host: Vostro 5590 Kernel: 5.15.10-100.fc34.x86_64 Packages: 2607 (rpm), 11 (flatpak) Shell: bash 5.1.0 Resolution: 1920x1080 DE: GNOME 40.6 WM: Mutter WM Theme: Adwaita Theme: Adwaita [GTK2/3] Icons: Adwaita [GTK2/3] CPU: Intel i7-10510U (8) @ 4.900GHz GPU: NVIDIA GeForce MX250 GPU: Intel CometLake-U GT2 [UHD Graphics] Memory: 3812MiB / 23816MiB

I uncheck the option in the red circle and the last 3 tabs that I opened are not at 100%. see screenshot

.....

Thanks for the reply, hope you're having a great new year :)

Perhaps I'm being silly, but I can't find where you're finding that red circle? I don't have that configure button on the sound settings....