It wasn’t json parsing per se, but a buggy roll-your-own implementation that used a function (sscanf iirc) with a surprising nontrivial complexity on a long string. Fun part is, if they just outsourced that load to javascript and its JSON.parse, they’d never encounter that exponential slowdown. Javascript is a nice target to blame, but it isn’t the problem. CPUs got hundreds of times faster, javascript only divides it by N, which stays low and constant (at least) through decades. Do you really believe that if browsers only supported MSVC++-based DLLs without scripting, sites would run faster? That would be naive.