The problem is *only* to do with graphics card drivers. See this blog post and this followup. It is literally not affected by anything else, it doesn't matter what CPU or how much RAM you have, if your graphics card driver is blacklisted it won't use the graphics card to render and the game will be slow. (All modern browsers support rendering on the GPU.)
If you read the blog post you'll see it's out of our hands really - many graphics card drivers are crap, so users need to update to get good performance.