Web browser in DeoVR is called "Mono Browser". It was written in mono. It was not made by millions of coders like other browsers, so its features are limited, and lots of today's website, which heavily depends on javascript, will not work well with the limited Mono browser in DeoVR.
Plus DeoVR itself has put some limitations on the mono browser, making it less useful.
So you should use DeoVR's browser to watch the websites that's designed for it, like SLR, and not other websites which requires latest web engines.