How to analyze the power usage of websites in Firefox

Mozilla launched Firefox 104 recently, and with it a new Developer Tools option to analyze the power usage of websites. The feature is limited to Windows 11 and Apple M1 devices.

Power usage of devices has been in the focus for some time, but not on which activities require the most power on a device. The information may be useful, especially for mobile users who run their devices on battery sometimes or all the time. If battery is getting low, one could extend battery life by avoiding power hungry activities on the device.

To measure the power usage of websites in Firefox, Firefox 104 or later is required. This is the only prerequisite, other than running Firefox on a Windows 11 or Apple M1 device.

Note: the data is submitted to the Firefox website, where it is displayed.

power usage websites

Here are step-by-step instructions to check a website’s power usage in Firefox:

  1. Open the website that you want to analyze.
  2. Select Menu > More Tools > Web Developer Tools, or use the keyboard shortcut Ctrl-Shift-I to open the interface.
  3. Optional: I suggest you move the interface to the bottom of the Firefox window by selecting Menu > Dock to Bottom.
  4. Switch to the Performance tab in the Developer Tools interface.
  5. Select the Power option under Settings.
  6. Activate the “Start recording” button.
  7. Use the website as you would normally.
  8. Activate the “Capture recording” button to end the recording.
  9. The Firefox Profiler website is loaded automatically.
  10. Locate the Power readings at the top (you may need to scroll down to find them).
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Firefox lists how much CPU package, CPU cores and iGPU power the website required during usage. Move the mouse over the data to get the actual reading, e.g., 6.89W at the 10 seconds mark.

The new profiler option lacks information. Is 6W much when it comes to websites? There is no average that Firefox displays, which could be useful, or different power usage ranges that reveal whether a site is draining more power than the average site or less.

For now, Firefox users are left alone in the quest. Checking multiple sites may reveal the missing information, so that it becomes easier to determine if a site is draining more power than the average.

Now You: how much power do your favorite sites require?