I just loaded up Netscape 9 (the oldest one I could get to run without too much digging) and while it is quite quick for average pages, a stress test like jsfiddle.net/4dpGz froze it up for several minutes. (It also doesn't render correctly, but I think that's a separate issue.) FF57beta finished in 10 seconds. Firefox 0.6 just says "connection refused" to most sites, so that's pretty fast :p