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.

Answering my own question. The problem was solved like this: about:config privacy.resistFingerprinting privacy.resistFingerprinting.pbMode False Now the time in the browser and the local time aren't different