That's very odd - are you sure it's not just because when you're zoomed in less of the game is showing actually on-screen? Anything offscreen generally isn't drawn.
No - this is legitimate enough.
Try it yourself, it just has to be in full screen of course. Set the browser to 100% and full screen, then try setting it to 200% and try again. The rendering quality is lower, but performance GPU wise is almost doubled.
This is the perfect way to scale quality vs. performance.
So I would love the Browser plugin to have a zoom setting. I am very surprised this is new to you :D