Best Open Source Browser with Xul Support - Waterfox

Waterfox 6.6.9 is the best open source browser with XUL support for Windows users who need legacy extension compatibility.

Built directly on Firefox's codebase, Waterfox maintains full XUL extension support while modern browsers dropped it years ago. This makes it the go-to choice for developers and power users clinging to their favorite old-school add-ons. The browser handles performance optimization specifically for Windows, so you're not just getting nostalgia — you're getting speed.

Why XUL Support Matters

XUL (XML User Interface Language) extensions created the golden age of browser customization. Modern Chromium-based alternatives and newer Firefox versions abandoned XUL, leaving users stuck. Waterfox keeps that legacy extension support alive. If your workflow depends on extensions that haven't been updated since 2015, this open source browser is literally your only option.

No compromises needed.

What Makes Waterfox Stand Out

This Firefox alternative goes beyond basic compatibility. The developers optimized it specifically for Windows performance — faster startup, lower memory usage, snappier tab switching. You're not running bloated code; you're running a , developer-friendly version that respects your system resources.

As an open source project, Waterfox's code is transparent and community-audited. Want to check what it actually does? You can. Want to contribute improvements? You can do that too. It's customizable at every level, which appeals to the same crowd that loved XUL in the first place.

The Practical Reality

Version 6.6.9 delivers exactly what it promises: XUL support, Windows optimization, and zero licensing fees. If you're upgrading from an ancient Firefox installation or switching from a discontinued browser, Waterfox bridges that gap .

Download it for Windows and keep your legacy extensions running. Problem solved.