Like Google Chrome, Opera, and Edge, Mozilla Firefox browser also allows you to change the default background theme.
How to Change the Theme of Mozilla Firefox Browser?
1. Open the Mozilla Firefox browser.
2. From the right side top corner, click on the “Open Menu” icon.
3. Click on Add-ons.
4. Click “Get Add-ons” from the left-side menu and scroll down till you get “Featured Themes.”
5. Click on the “See all” link next to Featured Themes.
Here you can see the thousands of themes for your Firefox browser.
6. Click on any theme, which you like to install.
In my example, we have selected the “Two little birds” theme.
7. Click on “Add to Firefox.”
8. Selected themes will be downloaded and applied as the default theme for your Mozilla Firefox browser.