Insane CPU usage (and lag) when visiting a game-series page

[Lordmau5]

Before going into any details, I should mention that this only happens when I am logged in.

When visiting any game-series page, be it the one for Super Mario or Densha de D, my CPU usage is skyrocketting upwards of 40% (reached 60% even at some point).
Those pages also take an unusually long time to load to begin with.

I've also noticed that on subsequent visits, the CPU usage isn't ramping up as high anymore as previously, probably due to certain parts of that page being cached already.

These issues do not occur when logged out or using an incognito window (tried in both Chrome and Firefox).