I think the jump height does vary with the framerate.
Jumping is just projectile motion and you can calculate mathematically the jump height with this formula:
jump_height = (jumpStrength^2)/(2 * gravity)
In the case of the example the calculated jump height should be 50 pixels.
When I ran the capx I measured the jump height and it was 56 pixels. On my machine it was running a about 30fps.
The platform behavior currently changes the y position like this:
y = y + v_velocity * dt
If it's changed to this:
y = y + v_velocity * dt + 0.5 * gravity * dt * dt
Then the measured jump height will match the calculated jump height regardless the framerate.
@Ashley my proposed fix is to change this:
..\Construct 2\exporters\html5\behaviors\platform\runtime.js lines 582-583
this.inst.x += this.dy * dt * this.downx;
this.inst.y += this.dy * dt * this.downy;
this.inst.x += (this.dy * dt + 0.5 * this.g * dt * dt) * this.downx;
this.inst.y += (this.dy * dt + 0.5 * this.g * dt * dt) * this.downy;