Of course, but you'd think after 30 years the compute power should be enough to overcome any lack of optimization. It's a testament to the engineering that went into the original Quake engine.
Err, strange, what browser? I'm using Firefox on a ThinkPad from 2018 running Linux, and cssquake was running at a smooth 60fps just now (and at 1080p resolution vs the 320x240 or 320x200 someone would likely be running on a P133)
Most of the time, things seem to be optimized for Chrome, but with this, I actually had the impression that Firefox ran a bit smoother, but I tested it on Linux.
