I have three monitors in landscape surround, and I have been wondering if there is a way to fullscreen sites like youtube or netflix on a single one of my monitors, preferably the sides, without affecting the other monitors? Currently when I try, the window in question jumps to my middle monitor and blacks out the sides, youtube being notably the worst, in that it stretches the entirety of the youtube control panel across all three monitors. I currently have Display fusion set up to logically split the surround setup into their three respective monitors via the build in monitor configuration. Is there a setting I have missed that allows me to fullscreen things like netflix and youtube within a single split?

As an added note, I have noticed my internet browsers are the most behaved of my programs when it comes to display fusion, but things like steal, when dragged to the side of my side monitors does not snap to fullscreen on only that monitor like my browsers, instead it tends to snap to exactly half my 5760x1080 resolution, and cuts down the center of my middle monitor

I currently use firefox, but I am thinking about getting waterfox. is there an addon I can run that would enable this?