effectAllowed is returning "uninitialized" on firefox browser

I created a **isCopy** to dectect if copy or move drag event. to simulate, ctrl + drag item then drop.

export const isCopy = (event: React.DragEvent) => event.dataTransfer.effectAllowed === "copy".

it works on google chrome. But in the firefox browser, it is returning uninitialized. See the image below