Don&#x27;t be ridiculous, the rendering engine is much more complex and many more lines of code than the GUI features. And browsers have had bookmarks, tabs, and password managers for a decade now.<p>More importantly, the rendering engine is what matters to the &quot;open web&quot;, if you care about that. If there&#x27;s only one rendering engine which &quot;everyone&quot; uses, then websites are designed to the bugs and quirks of that engine, then that engine need not fix any bugs, then those bugs become the de-facto standard. Then users can&#x27;t use the web from the platform or browser UI of their choice if the only web rendering engine of note doesn&#x27;t support it.