The OP isn't talking about rendering (at least as I understand it, which isn't well either), it's talking about why, after rendering, it takes so long to switch between tabs or why creating a new clean tab takes more than a millisecond.
I, like the OP, don't understand why that part is hard. Does it have to rerun and redownload all the javascript each time you switch to a tab? Are we misunderstanding how websites work? Will removing all JS solve the behavior the author mentions? Obviously doing that will make pages load faster. But that's not what they seem to be asking. Is the OP question not meaningful because of some aspect of page rendering?
Honest questions, I have basically no knowledge about this topic, but have wondered the same thing.
I, like the OP, don't understand why that part is hard. Does it have to rerun and redownload all the javascript each time you switch to a tab? Are we misunderstanding how websites work? Will removing all JS solve the behavior the author mentions? Obviously doing that will make pages load faster. But that's not what they seem to be asking. Is the OP question not meaningful because of some aspect of page rendering?
Honest questions, I have basically no knowledge about this topic, but have wondered the same thing.