It sounds like Firefox may be set to resist fingerprinting. Some websites use fingerprinting to try and uniquely identify you when you visit the website. They use a big list of things like your timezone to try and do that. If Firefox is set to resist fingerprinting, websites would only see your timezone as UTC time. This can cause some times to be displayed incorrectly on certain websites. To disable resist fingerprinting, please refer to the [[Resist Fingerprinting]] article. Hope this helps.