This has happened for so long and is what is keeping me from using Firefox, making me want to uninstall it sometimes.

Most people don't leave their Volume Mixer open, but some do, and I rely on it quite a lot. Wasn't too much of an issue because it only happened when I used Firefox. Recently.. Starting some several months ago maybe even a year. Firefox will now create instances in the Mixer even without launching it. I haven't used it in weeks and yet every day there's more instances in my mixer.