Go to about:config and make sure privacy.resistFingerprinting is default false.

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile.

WARNING from the moderator team: Changing Firefox preferences from the about:config page can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing. Please read Firefox Advanced Customization and Configuration Options to learn more.

It didn't fix the problem. Odd thing is that my ios Firefox's time zone is correct.

Which website are you using to check the time?

A few countries (such as the UK) change their clocks around this time of year by an hour.

Are you using a proxy or VPN?

You can check the connection settings.

• Settings -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet, select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors
• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can
• https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

No VPN I am using Firefox on macos sonoma 14.0. I am also using Firefox macbook pro mid 2012 macos catalina, and the time zone works just fine. The website has the correct time zone, in all browsers, except Firefox. Deleted and re-installed firefox multiple times, clear history, cookies, cache. The time zone is still one hour behind. I allowed for the site to use my location. Then I blocked. Problem persists.

The website

Do you see this on a different website like https://webbrowsertools.com/timezone/?

I tried all the options from the drop-down list. The time was 1 hour behind than mine. It must be a problem with Firefox and macos sonoma. Because every other browser and app is in sync.

This is not caused by the privacy.resistFingerprinting since I have it set to False.

I have this same issue. When searching for the issue on the internet, I found that this is related to MacOS Sonoma indeed. In my machine only Safari displays the time correctly. Both Firefox and Chrome are 1 hour behind. I tested this by visiting https://everytimezone.com website on the three browsers.

This hasn't broken web browsing. However, in apps such as MS Teams, Gmail, Slack, etc., where message times are displayed, all times are 1 hour behind.

At this point this is a known issue and I was able to see that Chrome will be fixing the root cause in their next update. It might be a low level OS API call that might have either changed or deprecated in MacOS Sonoma that can be causing this behavior.

Paste each of these one at the time in the command line, press Enter to see the result if Firefox doesn't already shows this after pasting/replacing.

• "3-bar" menu button or Tools -> Web Developer

(new Date());

(new Date()).toString();

(new Date()).toLocaleString("en-US",{weekday:"long",day:"numeric",month:"long",year:"numeric",hour:"numeric",minute:"numeric",second:"numeric",hour12:false,timeZoneName:"short"});

This should be fixed in Firefox 119 (Bug 1856428).