Software shouldn't be able to (and can't, I'm pretty sure) cause the hardware to literally overheat, such that it's damaged. But it can easily cause the hardware to become uncomfortably hot, because the hardware is more tolerant of high temperatures than squishy human flesh.

High CPU usage tends to make things hot and waste battery. I think it's just a matter of the browser not letting the CPU idle for whatever reason.

I do run AdBlock Plus though, and am hoping that content blockers in OS X El Capitan will help with this even further.

Have you owned a Mac laptop before ? The aluminium case is a giant heatsink and it's very common for applications to cause the laptop to become hot. Sometimes unbearable so.

It's well known that Safari is significantly better than Chrome when it comes to resource consumption. There are even some podcasts with ex maanagers of the Safari team where they talk about Apple prioritising battery life over anything else.