Chrome 69.0.3497.92 with performance related hotfixes just got released. Might want to re-run the available tests in here and see if it's fixed.
Might, improve it a bit. Canary was slightly less jank for me. But as this seems to be a power saving OS especially on laptops and such. I'm not sure how it can be improved really.
As someone else reported text object also quite a big factor. Not updating text every tick certainly helps quite a bit. At least for me.
Endless Runner in Firefox - Surface Pro 4, on battery, recommended power mode.
Disabling text update event, playable with a few janks here and there that seems to be related to GC and Vsync
Computer throttles down to low 0.5 Ghz or something like that. But when there's actually a major GC happening, it's throttled down so much that the CPU can't speed up fast enough again to do the GC, so you notice a quite significant jank.
Some minor dropped frames here and there seems to be v-sync. V-sync seems to fail more on battery, and power plans set to recommended settings.
What irritates me is that these power saving features ruins the experience. Imagine if you were watching youtube or a movie on battery power and the videos keeps janking. That would be unacceptable! There would be a public outcry probably. HTML5 games on the other hand, seem to suffer more from these power saving features, especially when in battery power.
As no-one seem to wanna touch the issue, there's not much else than inform your players to change power mode if they play your games on laptops, and notice bad performance.
Exported Mobile projects seem to be fine though, an occasional dropped frame here and there. But recommended not to use any text object that updates frequently.