---
id: fuzzfetch
version: "16.1.0"
license: MPL 2.0
license_treatment: copyleft
maintenance: active
---

# fuzzfetch — Downloader for firefox/jsshell builds.

License: copyleft · Maintenance: active · Downloads: 95.6K/mo

## What it is and what it does

Fuzzfetch is a command-line tool that automates downloading pre-built Firefox, Spidermonkey, and Thunderbird binaries from Mozilla's Firefox-CI Taskcluster service. It abstracts away the complexity of navigating Taskcluster namespaces and build metadata, letting you specify a branch, build date or revision, and build variant (debug, AddressSanitizer, ThreadSanitizer, fuzzing, coverage, etc.) and get the matching artifact. The tool supports multiple operating systems (Android, Darwin, Linux, Windows) and CPU architectures, and can search for the nearest available build if an exact match isn't found.

The package is designed for security researchers, fuzzing engineers, and developers who need to test against specific Firefox builds or variants. It depends only on pytz and requests, making it lightweight to install. The tool runs as a CLI with a rich set of options for targeting specific builds, and also supports dry-run mode to inspect metadata without downloading.

Use it for:

- Download AddressSanitizer or ThreadSanitizer builds for security testing and memory-safety validation.
- Retrieve fuzzing builds (AFL++, Fuzzilli, Nyx) for automated fuzz testing campaigns.
- Fetch debug builds of SpiderMonkey for JavaScript engine development and debugging.
- Obtain coverage builds to measure test coverage across Firefox test suites.
- Automate CI/CD pipelines that need specific Firefox or Thunderbird revisions for regression testing.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Fuzzfetch retrieves Firefox, Spidermonkey, and Thunderbird builds from Mozilla's Firefox-CI Taskcluster instance, supporting specialized build types like AddressSanitizer, ThreadSanitizer, debug, and fuzzing variants.

Yes. Fuzzfetch is actively maintained, has no known vulnerabilities, low install friction, and solves a real problem for anyone working with Mozilla builds. The MPL 2.0 copyleft license is standard for Mozilla projects and poses no barrier to internal use or testing. Install it if you regularly need to fetch Firefox, Spidermonkey, or Thunderbird builds from Firefox-CI.

## Install

pip install fuzzfetch
uv add fuzzfetch
poetry add fuzzfetch

## Installing fuzzfetch

Before you install: Low install friction with only two runtime dependencies (pytz and requests). The package is actively maintained with a recent commit on 2026-07-06 and has been in production since 2017.

License in practice: Licensed under MPL 2.0 (copyleft), which requires derivative works to disclose source code changes under the same license if distributed; acceptable for internal use and testing.

Quickstart:

pip install fuzzfetch

from fuzzfetch import Fuzzfetch

# Retrieve latest AddressSanitizer + fuzzing build
fuzzfetch -a --fuzzing

# Or retrieve debug build of JS shell
fuzzfetch --target js -d

Requires Python 3.10 or later.

Verify before relying:

- Whether builds are cached locally or re-downloaded on each invocation.
- Network timeout behavior and retry logic when Firefox-CI is unavailable.
- Disk space requirements for typical build downloads.

## Package facts

- License: MPL 2.0 (copyleft)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 95.6K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

firefox build downloader, mozilla taskcluster builds, fuzzing build retrieval, sanitizer builds firefox, mozilla-central builds, spidermonkey js shell, thunderbird build fetcher, mozilla-builds, fuzzing-tools, security-testing

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