sizcoz Tested your export. These are my results:
Surface pro 4:
Firefox: See very noticeable janks.
Chrome: 69, janky.
Canary: janky but a bit less.
Now here comes the twist though!
I connected the power cable because my surface was getting a bit low on battery. Hmmmmm....janks suddenly decreased quite a lot. Chrome 69 and firefox still had some, but not as frequent, and not as heavy. I thought, that's odd so i tried something else. I clicked the battery icon in the task bar, and changed setting to best performance.
Result after setting:
Firefox: no janks
Chrome: no janks
Canary: no janks
Are you testing on a laptop? or using balanced power scheme?
Results on Sony Xperia XZ1
Chrome: Some very rare janks far between.
Edge: Some occasional jank.
So on windows, power mode setting seems to make a huge difference. In other desktop games(non html5) this usually only lowers framerate when on battery, but does not cause janks.
I only have laptops, tablets and mobiles to test on. No regular gaming computer, workstation or anything like that.
I'll test on macbook pro when I'm back at work tomorrow.