[Bug-gnuzilla] JavaScript bug in Date class, incorrect date/time returned

[Jelle Geerts]

var s1 = new Date().toString();
var s2 = new Date().toLocaleString();
var s3 = new Date().toLocaleString('nl', {'timeZone': 'Europe/Amsterdam'});

The resulting strings were:
  s1 === 'Fri Jun 07 2019 13:58:32 GMT+0000 (UTC)'
  s2 === '6/7/2019, 1:58:32 PM'
  s3 === '7-6-2019 15:58:32'

s1 is not as expected (bug).
s2 is not as expected (bug).
s3 is as expected.

Expected output (taken from Firefox; Chrome has the exact same output):
  s1 === 'Fri Jun 07 2019 15:58:32 GMT+0200 (Central European Summer Time)'
  s2 === '6/7/2019, 3:58:32 PM'
  s3 === '7-6-2019 15:58:32'

Tested in a virtual machine on a clean install of Ubuntu 18.04 LTS.
System locale: en-US
System time zone: Europe/Amsterdam (which is UTC+02:00 at this moment)

Other browsers, such as Firefox, running on the same system as IceCat,
do return the expected output (no bug).

Also, websites seem to rely on (new Date().toString()) returning a
localized date/time,
as shown in the expected output.
Firefox and Chrome do this.

$ icecat --version
GNU IceCat 60.7.0