I was referring to the innovations in browser capabilities. Process sandboxing massively improved both the robustness of the browser experience and the boldness with which features could be used (because a crashing site wouldn't take the whole browser with it). It paved the way for the actual "browser is the OS for the web" experience we have today, unlike IE's attempt to wed a crash-prone application to its core OS functionality. As a result, the browser capability specs themselves exploded, which eventually rendered Flash, Silverlight, and ActiveX plugins mostly redundant and allowed browser vendors to make their way towards stripping them out in favor of web-engine-only solutions.