It works with everything! Basically I'm playing Club Penguin Journey and NO other Firefox volume extension would recognize the sounds played from that tab! This is the ONLY one that recognizes it and allows me to change the volume for it. I'd say my only concern is the "Access your data for all websites" thing (as it's a little known extension), which must be enabled for this to work. It'd be great to allow it to access only certain sites, but not all sites. Anyhow, thank you so very much daveyj!