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Firefox 14 may break your theme

The latest version of the desktop browser is incompatible with a huge number of existing themes.

screenshot by Lance Whitney/CNET

Firefox users who've installed a custom theme may bump into trouble if they upgrade to the latest version of the browser.

Released earlier this week, Firefox 14 offers a few enhancements, including better security. But it comes with one gotcha -- lack of support for a lot of existing themes.

Many Firefox users probably know that they can change the style of their browser by installing one of many custom themes, available at the Themes section on Mozilla's Add-Ons page. You can choose from among hundreds of different themes to customize the look and feel of Firefox's menus, toolbars, and overall background.

I used a theme called MacOS X, which offered a simple but sleek look to the browser based on the style of Apple's OS X. But when I installed Firefox 14, I received an alert that the theme would not be compatible with the new version. I moved ahead with the install anyway, and afterwards Firefox reverted back to its default theme.

In search of a new theme, I scoured the Themes section only to discover a huge number unavailable for and incompatible with my new version of Firefox. The thumbnails for each theme tell you right up front whether it will work with FF 14, so at least you don't need to waste time clicking on every one. But finding a theme that you like and works with the new version can still present a challenge.

After trying a slew of compatible themes, I finally found one I liked, and the installation went smoothly.

Why are so many themes incompatible with Firefox 14?

One poster in a discussion board on Firefox suggested that the developers simply need to change the theme's compatibility on the Add-ons site.

But I've upgraded through several iterations of Firefox over the years and have never run into so many themes labeled as incompatible.

A spokeswoman for Firefox sent CNET the following statement from Johnathan Nightingale, director of Firefox Engineering:

The number of compatible themes has actually remained quite stable over the last three releases of Firefox, hovering around 140 in total. Themes can integrate deeply with the Firefox user interface, which makes them very version dependent. Because many themes are built by volunteers, they are not always updated in the days immediately after a new Firefox release.

So maybe it's just a matter of waiting for developers to catch up with the latest version.

Updated 10:30 a.m. PT with response from Mozilla.