My hackintosh with a dedicated GPU has no problem at all because it has the rendering power to handle it. But my 2014 MBP Retina with integrated graphics gets destroyed and ends up spiking the CPU as well.
I have the top of the line model from 2013 with 16GB RAM and discrete graphics (forced to always be used in energy saver prefs).
Firefox feels very fast and doesn't lag while being used, but the unnecessary CPU spikes kill my battery. We're talking about one page open at about:blank with no extensions and a completely fresh profile spiking to 20% CPU usage every 10 or so seconds.
