Firefox themes — also known as “personas” — can change the way your browser looks, making it more personal. If you like theming the applications you use, there’s no better application to theme than your browser.

This isn’t too hard — all you need to do is find a background image or two and crop them to the correct proportions. Chrome users can use Google’s easy Chrome theme creator to make their own browser themes.

Get Your Images Ready

RELATED: How to Easily Create Your Own Google Chrome Theme

A Firefox browser theme is made up of two images. There’s a header image displayed behind everything at the top of the Firefox window, and a footer image displayed behind the Find and add-on bars at the bottom of the window. The latest versions of Firefox remove the add-ons bar unless you install an extension to bring it back, so the top image is much more important. You’ll only see the bottom image when you press Ctrl+F to use the Find toolbar. Visit the Themes gallery to see pre-made Firefox themes you can use.

First, find a good-looking image that will work well on your top toolbar. Mozilla advises that “Subtle, soft contrast images and gradients work best; highly detailed images will compete with the browser UI.” The top-right corner should also have the most interesting bit of the image, as the top-right corner of the image will always be displayed in the top-right corner of your browser. As you resize the browser window, more of the left side of the image will become visible.

Here are the exact image specifications required:

  • Header Image: 3000 pixels wide x 200 pixels tall, PNG or JPG format, 300 KB maximum file size
  • Footer Image: 3000 pixels wide x 100 pixels tall, PNG or JPG format, 300 KB maximum file size

You’ll want an image of at least 3000 pixels wide in size to start with. With a sufficiently large image found, all you need to do is crop it to the current proportions. Many desktop image editors (like the excellent Paint.NET) can do this, as can online image editors (like the convenient Pixlr Editor).

For example, in Pixlr, you’d open your image, select the rectangular selection tool, select “Fixed size” in the Constraint box, and enter a width of 3000 pixels and a height of 200. You could then select an appropriately sized area of the image. (Of course, you could also resize your image before cropping it in this way.)

You’d then crop your image — select Image > Crop in Pixlr — and you’d end up with a correctly sized image. You can now save it to your computer (File > Save in Pixlr). Repeat this process if you want a footer image, but make sure it’s only 3000×100 instead of 3000×200.

Enable and Configure Your Custom Theme

To create a custom theme without submitting it to the Mozilla themes website, install Mozilla’s official Personas Plus extension. Restart your browser after installing it, click the Personas Plus icon on your toolbar, and select Preferences. Activate the “Enable custom personas” checkbox and click OK.

You can now click the Personas Plus icon on the toolbar, point to Custom Persona, and click Edit. This will take you to a window with a simple interface to specify your images and desired text colors. Use the options here to browse for the header image file you created earlier and it will automatically appear on your Firefox toolbar.

Note that the footer image is optional — you’ll really only see if when you use the Find bar these days. If you don’t select a Footer image, the Find bar will just look like a normal part of the interface without any themes. Most people will probably be happy with that.

Select appropriate text and accent colors to make the browser’s toolbar text and icons stand out.

The resulting theme will work on every operating system, whether you’re using Firefox on Windows, Linux, or Mac OS X.

If you’d like to submit your theme for other people to browse, install, and rate on the Mozilla add-ons gallery website, use the Submit a New Theme page on Mozilla’s website. You’ll need to create a developer account first.

Profile Photo for Chris Hoffman Chris Hoffman
Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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