If the minutes are right but the hour wrong it's probably because your computer is set to the wrong time zone.

As for how to correct it, it's hard to say as you haven't said what operating system you use. In general a good start would be to right-click the clock and choose Properties, Preferences or something similar.

If you have enabled "Resist Fingerprinting", set this pref in about:config to false to disable this feature.

• privacy.resistFingerprinting => false
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox
• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

Note that enabling RFP sets you in the GMT/UTC timezone.