Could someone explain why running the below snippet on https://google.com results in different output than https://source.chromium.org/? As far as I can tell neither are in quirks mode.

const target = new EventTarget()
target.addEventListener("f", () => {
    console.log("f");
    queueMicrotask(() => console.log("f mt"));
});
target.addEventListener("x", () => {
    console.log("x");
    queueMicrotask(() => console.log("x mt"));
});
target.dispatchEvent(new Event("f"));
target.dispatchEvent(new Event("x"));

google.com logs

f
x
f mt
x mt

while source.chromium.org logs

f
f mt
x
x mt

Seirdy: W3C is theoretically mostly still on IRC, although it's fragmented a bit. You can bridge from matrix to the IRC server if you want to have a single interface.

I think the answer to "are questions about W3C specs welcome here" is "it depends on the spec".