We have various date selection widgets on our website, using a calendar picker format. But when the date is actually displayed as a date, Firefox (Mac) always shows it in US format rather than UK format. My other browsers - Safari and Chrome - correctly show the UK format. My Mac OS uses the UK format. Our developers say the HTML5 date pickers in Firefox and Chrome follow the computer's locale settings, and that it's not possible for them to specify a format in the code. If that's the case, why does Chrome correctly show the UK format but Firefox doesn't? I've checked the locale info in Firefox - here's what it shows: Internationalisation & Localisation Application Settings Requested Locales ["en-GB","en-US"] Available Locales ["en-GB","en-US"] App Locales ["en-GB","en-US"] Regional Preferences ["en"] Default Locale "en-GB" Operating System System Locales ["en"] Regional Preferences ["en"] If I can't fix this I'll have to stop using Firefox as my default browser because the date format causes too much confusion. It's heavily used for admin functions on our website, and I need to know at a glance that 01/10/2019 is 1 Oct rather than 10 Jan