Web Technologies Polyfill

Palefill Web Technologies Polyfill Add-on

Palefill is an add-on for Pale Moon that injects polyfills into pages to improve compatibility.

Check out the Github Releases for changelogs and news.


Polyfills are specified as “fixes” that are applied based on selector rules. Fixes currently can be:

It is possible to specify any combination of required fixes for a site. See the technical documentation for more details.


Supported Platforms

Palefill is developed and tested on the most recently released version of the Pale Moon browser. New features and fixes always target this browser and the then-current state of the web.

Contributors have also helped with Iceweasel-UXP, Basilisk and SeaMonkey support. Those are considered “mostly supported”.

It is also possible to install Palefill on any browser using the UXP toolkit. This should help with some more niche projects or custom and testing branches. Due to implementation details, it is technically also possible to install the addon on very old Firefox versions – this is caught at runtime since this won’t actually work.

When running in this compatibility mode, all features should still work as expected, but users should be aware that this is completely untested and no claims at all are being made. In this case, a warning text is displayed in the add-on’s preferences.


This add-on is heavily based on GitHub Web Components Polyfill, which does the same thing for GitHub and a few other sites.

 Portions based on GitHub Web Components Polyfill Add-on
 Copyright (c) 2020 JustOff. All rights reserved.
 Copyright (c) 2022 SeaHOH. All rights reserved.

The polyfills themselves have different contributors, see lib/polyfills.js.

The following people have contributed to this add-on: