Different browsers may have different interpretations of "locale" in Javascript, for example when using toLocaleString.

In the example above - at the time of writing anyway (March 2021) - I got these results:
Both Edge and Chrome returned "en = 24:00", while Firefox returned "en = 00:00".
All three returned "en-GB = 0:00".

I say "at the time of writing" because I'm 100% sure that Chrome returned "en = 00:00" until a while ago...
The change in behavior became apparent in code that had been working fine for about 2 years, but was now broken because of this. Switching to "en-GB" solved the issue on all browsers. Until the next update, anyway...

Region

Identification
	Sequence	10
	Title	Locale at midnight
	Type	Static Content
Source
	Source Type	STATIC_TEXT
	Region Source	<script> let d = new Date('1995-12-17T00:00:00') document.write( 'en = ' + d.toLocaleString('en' , {hour12: "", hour: "2-digit", minute: "2-digit"}) + '<br/>' ); document.write( 'en-GB = ' + d.toLocaleString('en-GB', {hour12: "", hour: "2-digit", minute: "2-digit"}) + '<br/>' ); </script>