Download websites that use Prefix-Free

About Prefix-Free

The name describes the stylesheet rather than the script. A developer using Prefix-Free writes plain CSS with no vendor prefixes in it, and the script is the thing that puts them back. What the file is good for now is dating the page it sits on.

Prefix-Free is a small JavaScript polyfill by Lea Verou, released under the MIT license and in circulation since 2011, which reads the browser's own capabilities at runtime and adds vendor prefixes to the CSS properties that still need them. In the era it was written for, supporting several rendering engines meant writing every gradient, transform and transition over and over with different vendor spellings, and a script that did the prefixing automatically saved real work. Then browsers converged. The problem the library solves has largely stopped existing.

Which is precisely why the Miscellaneous entry earns a place in a dataset. A page still shipping Prefix-Free is not making a technical choice, but carrying a decision nobody has revisited. The script marks a front end written when prefixing mattered and not rebuilt since, and that marker correlates with a stack of other things: unpatched dependencies, an ageing content management system or theme, no build pipeline, and often no active developer at all.

Which makes the list valuable to people with no interest in CSS whatsoever. Security researchers use abandonment markers to find sites that will not be patched when something breaks. Agencies use them to build redesign prospect lists, on the theory that a site frozen in an earlier era belongs to an owner who may finally be ready to spend. Performance and accessibility auditors use them to explain why a page behaves the way it does. Anyone studying how the web ages needs measurable fossils, and a library with a clear beginning and a clear obsolescence makes a good one.

As of October 2026 we detect Prefix-Free on 728 sites, and the honest reading of that count is uncertain in both directions. The script is sometimes bundled into a larger file where a fingerprint scan will miss it, and it is sometimes left in a template that still serves the file while nothing calls it. Detection sees delivered code, not executed intent.

A single lookup is close to meaningless for a signal like this. One site using an obsolete polyfill is trivia. A whole population of them, sorted by platform, country domain and what else they run, is a map of the part of the web that has stopped moving, and a map like that only exists if the entire set can be downloaded at once.