RRWeb only records changes to the DOM, it doesn't actually replay the JavaScript that makes those changes happen. So you see exactly what the user sees, but you're not able to inspect memory or anything like that.

There are a few caveats since not everything is captured in the DOM, such as media playback state and content in canvases. The user may also have some configurations that change their media queries, such as dark mode or prefers reduced motion.

Edit: and yes, to your point, browser differences would also render differently.