Bad performance on HTML5 single page spec

[NiLSPACE]

On the HTML5 single page spec I'm only getting ~6 fps if I'm lucky.

After scrolling for a while it's also using 3GB of my RAM.

Command used:
servo -Z wr-stats https://www.w3.org/TR/html5/single-page.html

Specs:
CPU: I7 6500U @ 2.5GHz,
RAM: 16.0GB Dual-Channel,
GPU: Intel HD Graphics 520
OS: Windows 10 PRO 1607

Since I'm using the nightlies on Windows it means this is an old build.

EDIT:
Same happens with Linux.

[NiLSPACE]

I'm currently seeing way better performance, but the memory usage is still really high and the CPU usage goes to 70% when you start scrolling.

[NiLSPACE]

I noticed that when resizing the Servo window it takes quite allot of time for Servo to adjust the page and move the scroll bar over to the right.

[NiLSPACE]

I noticed that the CPU usage only goes up really high when the cursor is inside the page. When the cursor is outside Servo the CPU usage drops to 0 after a while, but the moment you put the cursor back the CPU usage goes high again.