I had another look at the link I posted and, more importantly, another coffee, and I feel I should clarify what I was doing and what all those numbers mean.
My issue was with having 144 hz refresh rate, which made the program run faster under certain conditions, but more importantly causing the character in a simple test program jump to a different maximum height.
This jump height is what the numbers in the last four columns mean, around 520 being the intended value and highlighted in yellow. The four rightmost columns show jump height with 144 hz refresh rate (normal build and html5) and then with 60 hz set (again, normal build and html5).
Setting my desktop refresh rate to 60 hz helped me, but that’s obviously not a great solution if you want other people play to play the game as intended.
I believe I ended up relying on go.animate to move stuff exclusively, rather than using dt, which fixed this across the board, since I didn’t really feel great limiting the frame rate. It’s been a while, though, and VSync has always been one of those things I’ve stubbornly refused to understand, so I I can’t really say much else on this topic.
Here’s the relevant thread, plus there’s a whole bunch of others if you search for “vsync”.