David Baron's Weblog

How you can help with removing -moz- prefixes

Monday, 2013-02-25, 17:25 -0800

At Mozilla we value the Web having content that works across multiple browsers. This allows competition between browsers, which leads to better results for users of the Web.

Recently vendor prefixes have contributed to content that doesn't work in multiple browsers. We've been working on using prefixes less. But we still have the problem of removing support for vendor-prefixed properties that we currently support. We want to remove this support because we don't want the Web locked in to Mozilla-specific content. But when we remove support for features, it does sometimes break pages.

We've supported unprefixed CSS Transforms, CSS Transitions, and CSS Animations, and the border-image property, for a while now. So at some point soon we'd like to remove support for the older -moz- prefixed forms. Since these properties were commonly used, I've added code for user preferences that allow authors and users to test that pages work correctly once the support for these prefixed properties is removed.

These preferences, introduced in Firefox 19, are:

and they can be modified by going to the URL about:config in Firefox, searching for css.prefixes, and toggling the preferences to turn off support for these prefixed properties (while leaving support for the unprefixed properties):

[image showing about:config in Firefox, with a search for 'css.prefixes']

You can help the Web remain browser-agnostic by testing with these preferences to make sure pages that you've written, or pages that you care about, work correctly without these browser-specific properties (by using their unprefixed forms).

Update (17:35): I realized that the patch doesn't disable support for @-moz-keyframes. I'll get that change in to Firefox 22; until then, it's probably not worth testing the layout.css.prefixes.animations preference extensively.