Yes, you can use an extension, for instance Tabliss.

Hello,

Welcome to the Firefox Support Forum! I'm glad to hear that you're switching to Firefox from Chrome. In Firefox, you can customize your new tab page, including setting a custom background image as a wallpaper. Here's how you can do it:

Open a new tab in Firefox. Click on the gear icon (settings) located at the top-right corner of the new tab page. In the menu that appears, select "Customize". This will open the customization options for the new tab page. Look for the "Background Image" section. Click on the "Choose..." button to select an image from your computer as the background wallpaper. Once you've selected the image, it will be set as the background for your new tab page. That's it! Now you can enjoy a personalized wallpaper on your Firefox new tab page. If you have any further questions or need additional assistance, feel free to ask. I'm here to help!

Best regards, Suram Firefox Support Volunteer

Click on the gear icon (settings) located at the top-right corner of the new tab page. In the menu that appears, select "Customize". This will open the customization options for the new tab page. Look for the "Background Image" section.

This does not exist. You need to test suggestions before posting them.

Apparently he just uses ChatGPT to answer without any testing. And Chat made up that answer.