How to Show Multiple Time Zones in Firefox (World Clock Guide)

If you want to know what time it is in multiple time zones simultaneously without switching apps or opening a separate website, Firefox has built-in options and extension options. Here's what actually works.

The Built-In Firefox Option (None)

Firefox doesn't have a built-in multi-timezone clock widget. This is a gap that extensions fill.

Option 1: New Tab Extension with World Clocks

The most convenient approach: replace your new tab with a page that shows multiple clocks. Every time you open a new tab, you see the current time in each configured time zone.

Weather & Clock Dashboard supports configurable world clocks alongside live weather. You add cities once, and every new tab shows their current time.

Setup:

1. Install from AMO: link
2. Open a new tab
3. Click the settings/gear icon
4. Scroll to "World Clocks" section
5. Type a city name and add it (example: "London", "Tokyo", "New York")
6. Clocks appear immediately

Why this works well: You open new tabs constantly throughout the day. Seeing the world clocks passively — without any deliberate action — builds intuitive awareness of the time difference without active lookup.

Option 2: Firefox Sidebar with a World Clock Site

Firefox's sidebar can display any website. You can load a world clock site in the sidebar, which stays visible across all your tabs.

To add a website to the sidebar: some sidebar extensions allow this. The Sidebar Web Panel extension can load worldtimeserver.com or timeanddate.com in a permanent sidebar.

Downside: Sidebars take up horizontal screen space, which is more valuable than vertical space on modern widescreen monitors.

Option 3: Pin a World Clock Tab

The simplest option: go to worldtimeserver.com or timeanddate.com/worldclock/, configure the cities you want, and pin the tab.

Downside: You have to actively click to check. The new tab approach gives you passive awareness at no extra cost.

Adding Specific Cities

For the new tab extension approach, you can add any city in the world. If a city isn't recognized:

• Try the country capital (Tokyo for Japan, London for UK)
• Try a larger nearby city
• Try the city's English name (Munich rather than München)

The extension uses a timezone database to compute the correct local time, including handling daylight saving time automatically.

The Daylight Saving Time Edge Case

The world clock shows the actual current local time, computed from the real-world offset at this moment. During daylight saving transitions (which happen on different dates in different countries), the displayed time automatically adjusts — you don't need to update any settings.

This is why a dynamic clock (via extension or website) is better than a fixed-offset calculation you do mentally. The current offset between US Eastern and UK times is different in October than in March.

For Distributed Teams

If you manage a team across time zones, the practical setup:

1. Add each team member's city to your world clocks
2. Check it passively throughout the day
3. After a week or two, you develop intuitive awareness of "it's 3pm for me, so it's early morning for Singapore"

The passive repetition of seeing the times daily builds a mental model faster than any deliberate study.