Reduced precision of `performance.now()`

[dgeb]

Firefox started rounding performance.now() timestamps to 1ms to mitigate security threats such as Spectre. Thus, results appear to be less precise in Firefox than Chromium by default.

It's possible to disable Firefox's privacy.reduceTimerPrecision preference to improve timing precision (this can be done from about:config).

See https://developer.mozilla.org/en-US/docs/Web/API/Performance/now