There is no reason for a modern browser to support Java, Flash, ActiveX-based or other content plugin that you call it. There is no reason that webpage content, no matter how dynamic, should use one of those in 2018. Those pages should be rewritten or die.I mean heck, the browser doesn't even support demanding video and interactive content plugins. Literally a text and image browser only...HTML is lightweight.
HTML5 content, ECMAScript 7 (or atleast version 6) as well as all image/video/fonts normally used on the web should be enough to view all new content.
And the ECMA VM should be fairly new as there were lots of improvements to the JIT performance around 2010-2012. Obviously the current browser is a really old codebase that at most supports ECMA 5 with a slow/old parser, and lacks support for most content types.