Just look at this Phaser example animation. Run it in Chrome (Version 79.0.3945.88, released Dec 17, 2019), then run it in Firefox or another browser.
Make sure to CLOSE the one running in Chrome when you go test in another browser, because whatever mischief Chrome is doing seams to drag the whole system when a Phaser file is running.
This is kind of important: Windows 7 reaches end of life next week.
Whether or not you are able to address the bug that kills your performance, you’re in for a world of trouble down the road if you continue to use an operating system that won’t get regular (or any!!) security updates. Not saying you should upgrade to Windows 10, but at least migrate to an OS that won’t make you a big target for hackers, viruses, and botnets.
From the horse’s mouth:
I can’t speak for the phaser devs but I suspect supporting dead operating systems is very low priority, if it’s even on their radar at all.