Designer Ilya Birman writes: I understand why rendering a complicated layout may be slow. Or why executing a complicated script may be slow. Actually, browsers are rather fast doing these things. If you studied programming and have a rough idea about how many computations are made to render a page, it is surprising the browsers can do it all that fast. But I am not talking about rendering and scripts. I am talking about everything else. Safari may take a second or two just to open a new blank tab on a 2014 iMac. And with ten or fifteen open tabs it eventually becomes sluggish as hell. Chrome is better, but not much so. What are they doing? The tabs are already open. Everything has been rendered. Why does it take more than, say, a thousandth of a second to switch between tabs or create a new one? Opening a 20-megapixel photo from disk doesn't take any noticeable amount of time, it renders instantaneously. Browsers store their stuff in memory. Why can't they just show the pixels immediately when I ask for them? [...] Unfortunately, modern browsers are so stupid that they reload all the tabs when you restart them. Which takes ages if you have a hundred of tabs. Opera was sane: it did not reload a tab unless you asked for it. It just reopened everything from cache. Which took a couple of seconds. Modern browsers boast their rendering and script execution performance, but that's not what matters to me as a user. I just don't understand why programmers spend any time optimising for that while the Chrome is laughably slow even by ten-years-old standards.Do you agree with Birman? If yes, why do you think browsers are generally slow today?