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I believe they meant "runs directly on the browser without the need for additional plugins by using WebGL and WebVR".

Ah, got it. Human languages are so ambiguous. "One morning I shot an elephant in my pyjamas. How he got in there I do not know"

What are the plugins using WebGL and WebVR? I never heard of such plugins.

It means it doesn't need plugins because it's using WebGL and WebVR, which are baked into the browser.