" They are with Spectre and Meltdown mitigations. They are not new enough results to include anything for Fallout/ZombieLoad."
Not sure if including the latter mitigations would make AMD beat Intel in single threaded.
Firefox and chrome use a half-dozen or so threads parsing and compiling JS code so it loads quickly. Firefox's Quantum work adds a lot of threads for rendering as well. In addition, service workers, web workers, and Wasm all spawn additional processes which serve the same purpose if you aren't sharing memory directly.
That said, the Phoronix Selenium tests show AMD ahead by quite a bit. (source)[https://www.phoronix.com/scan.php?page=article&item=ryzen-37...]
Only in the narrow sense that processes are not threads. See `Window > Task Manager` in Chrome.
Basically, if the higher clock of the 9700K can be put to use in a single-threaded application, then that chip can still come out on top. But in enough scenarios, the Ryzen 3700X and 3900X are quite competitive.