That is interesting about Safari......on El Capitan my Mac Pro and 13" Retina froze with Safari open in moment when I close complicated tabs like YouTube, neverending Reddit etc...
I use USB mouse connected to one Thunderbolt Display and Logitech K811 BT keyboard.
Not directly related, but on the iPad/iPhone i encounter more and more freezing websites and finally a message at the top, saying "the tab has been reloded because there was a problem with the website" - all of them are "complicated" ones with a new annoying feature of some second layer publicity which displays as kind of background behind the text. (like a paper cut with holes...)