Invalid date error when manipulating dates with timezone plugin on Firefox and Safari

[sylvaindubus]

Describe the bug
I'm getting an Invalid date error when I try to manipulate timezoned dates on Firefox and Safari. It works as expected on Chrome. I am using startOf, but it seems that other manipulative methods are giving invalid dates as well.

Expected behavior
I'm expecting a valid date on all browsers.

Information

• Day.js 10.0.4
• Browsers: Chrome 89 (😎), Firefox 87 (🙁), Safari 14 (🙁)

Minimum code to reproduce it:

import dayjs from "dayjs";
import utc from "dayjs/plugin/utc";
import timezone from "dayjs/plugin/timezone";

dayjs.extend(utc);
dayjs.extend(timezone);

const date = dayjs().tz("America/New_York").startOf("month");

console.log(date.format());