Is it a website you could share a link to, that doesn't require a login? If the time format is determined locally by a script in Firefox, instead of on the server, Firefox ''should'' follow your regional settings in the Windows Control Panel. I have attached a screenshot for comparison. If the time is determined on the server, try clearing your cookies for the site in case the preference is somehow stored there. While viewing a page on the site, try either: * right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies" * (menu bar) Tools > Page Info > Security > "View Cookies" * click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually. Then try reloading the page. Does that make any difference?