onBeforeInput fires after browser updates the DOM for special characters like "中" or 😣on Firefox and Edge

[Chun-Yang]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
onBeforeInput fires after browser updates the DOM for special characters like "中" or 😣on Firefox and Edge
https://codesandbox.io/s/modest-franklin-muirj
NOTE: pasting it would not trigger the bug, you have to type it in. You can use control-command-space to open the emoji keyboard on mac

What is the expected behavior?
DOM should not update before onBeforeInput fires

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
React: 16.3.1
Firefox: 68.0.1
Mac: 10.14.5

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution.

[stale]

Closing this issue after a prolonged period of inactivity. If this issue is still present in the latest release, please create a new issue with up-to-date information. Thank you!