Personas are easy-to-use themes that let you personalize the look of your Firefox browser with fun colors and designs. This feature is integrated in the desktop Firefox browser, but was not available yet on mobile.
This is not the case anymore, as you can style your Firefox for mobile browser with the Personas add-on. No more grey in your browser!
To dress up your browser, install the add-ons from the mobile Add-ons Manager. You’ll see the Personas button your Start page. Just tap the button and go directly to the Personas web site to choose a theme, and wear it by tapping on the orange button. This will change your theme on the fly, and add it to your list of recent themes in the Add-ons Manager pane.
The theme will apply to the title bar, the Awesome Screen and tools panels, as well as to the Find in Page and Form Assistant toolbars. You can even use animated ones!