Software should be a malleable medium, where anyone can edit their tools to better fit their personal needs. The laws of physics aren’t relevant here; all we need is to find ways to architect systems in such a way that they can be tweaked at runtime, and give everyone the tools to do so.
It's clear that gklitt is referring to the ability of extensions to augment the browser, but: * it's not clear that he has applied the same thought process to the extension itself (which is also software, after all) * the conception of in-browser content as software tooling is likely a large reason why the perspective he endorses here is not more widespread—that content is fundamentally a copy of a particular work, in the parlance of US copyright law (which isn't terribly domain-appropriate here so much as its terminology is useful)