I have recently realized that I will occasionally hear notification sounds from applications that I had previously opened but no longer has any active tabs (email client, discord, etc.). I’m assuming this means they are allowed to keep some sort of connection in the background until I close all Firefox windows. Is this a bug or a “feature”? How do I turn it off? I don’t want any application running at any capacity except when I have tab(s) open for them.
Try using an addon like Basic Automatic Tabs Unloader, it will kill tabs completely a while after they’ve been closed. You can set the grace period as low as you want.
The Firefox native tab unloader is extremely permissive and only kills tabs when the whole system starts running low on RAM.