Firefox has been throttling background tabs (setTimeout, setInterval, requestAnimationFrame) for years. Starting in Firefox 55 there are more operations that a

Firefox has been throttling background tabs (setTimeout, setInterval, requestAnimationFrame) for years. Starting in Firefox 55 there are more operations that are being throttled. In both Firefox and Chrome the exact set of things that get throttled, and the throttling conditions, is somewhat in flux at the moment, as browsers try to figure out how much they can throttle without breaking legitimate usecases (e.g. user-desired audio in a background tab).