UXP is a fork of the Firefox 52 ESR platform, created in 2017 to address the imminent death of XUL/XPCOM technology in the Firefox codebase. Moonchild Productions develops UXP alongside Pale Moon. It includes the Goanna layout and rendering engine, a fork of Mozilla's Gecko engine. Pale Moon is built upon the Unified XUL Platform (UXP), a cross-platform, multimedia application base with ancestry in Mozilla code.

Uses the IP-API service instead of Google's for geolocation.Defaults to DuckDuckGo as the search engine instead of Google or Yahoo!.Defaults to a customizable start page in cooperation with.Always runs in single- process mode, whereas Firefox became a multi-process program.Replaces the Gecko browser engine with the Goanna fork.Supports NPAPI plugins indiscriminately, all of which are no longer supported by Firefox.Firefox no longer supports this and retains limited options for UI customization. Supports 'Complete Themes', add-ons which can customize the entire UI of the browser.Supports extensions built with XUL and XPCOM, which are no longer supported by Firefox.Uses the pre-Australis user interface ('Strata') as carried by Firefox during versions 4-28.Pale Moon has diverged from Firefox in a number of ways: With Tabs on Top enabled, Pale Moon most closely resembles the 'Strata' UI from Firefox 4-28.

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