The problem at hand is actually a pet peeve of mine and I really don't get why it's still the default to grant programs access to all our personal data. There is a lot wrong with mobile OSs, but in this regard they are actually ahead of the curve.
That's because our data has become a commodity relatively recently, and desktop technology still hasn't fully caught up yet. Regardless, it seems in general it's companies that run web services that are a bigger problem than desktop applications.
Either way, I'm glad projects like these exist, including snapd, flatpak, and this. The likes of flatpak and snapd may not be perfect, but it's progress.
I think you can check it in the snap metadata.
I was about to just use a plain docker for firefox and slack with mounted X11 file. This project tought me about a more secure method for X11 forward.