I am located in California / How do I make sure the Firefox I am using has the correct time zone for California?
You are using an old insecure version of Firefox. Time to update.
Firefox uses the "time" that as it is set in the Windows operating system.
You need to update a wide variety of things actually.
First, your Firefox. It is critically out of date, leaving you EXTREMLY vulnerable to MANY known security issues. Update Firefox to the latest version
Then, update your plugins. https://www.mozilla.org/plugincheck/
Finally, I bet Windows is out of date too. Update that: windowsupdate.microsoft.com/
Finally, date and time are controlled by your computer, not Firefox.
You can see the current time and time zone if you paste this code in the command line of the Web Console (Web Developer > Web Console; Ctrl+Shift+K)