Possible to Alter and Differentiate Between Media Audio/Sounds? What I mean by this question is if it's possible to mute one app that plays sound/audio directly to the media stream(?), and keep another app that is directly affected by the media sound slider with its audio/sound? 

For example: Spotify plays songs, but a video playing in Firefox is muted or independently altered to some degree. 

Sorry if this sounds a bit noobish, I'm new to this.
Unfortunately, this functionality is not yet available in Android. There is currently no way to separate apps that use the media stream. Your best bet would be to go to the app's settings and find a volume setting in there.