---
id: mozrunner
version: "8.4.0"
license: MPL 2.0
license_treatment: copyleft
maintenance: active
---

# mozrunner — Reliable start/stop/configuration of Mozilla Applications (Firefox, Thunderbird, etc.)

License: copyleft · Maintenance: active · Downloads: 246.3K/mo

## What it is and what it does

Mozrunner is a Python library for programmatic control of Mozilla applications. It abstracts the complexity of launching, configuring, and managing Firefox, Thunderbird, and other Mozilla tools as subprocesses, handling process lifecycle, profile management, and configuration injection. It's part of the larger Mozilla Mozbase toolkit and is commonly used in automated testing, CI/CD pipelines, and browser automation scenarios where you need reliable, repeatable control over application startup and shutdown.

The package depends on six Mozilla libraries (mozdevice, mozfile, mozinfo, mozlog, mozprocess, mozprofile) that handle complementary concerns like device interaction, file operations, system introspection, logging, and profile management. It supports Python 3.8 through 3.13 and carries no known security vulnerabilities. The copyleft license (MPL 2.0) means any modifications you make must be released under the same license, though using the unmodified package in proprietary code is permitted.

Use it for:

- Automated browser testing: launch Firefox with specific profiles and configurations for test suites
- CI/CD integration: reliably start and stop Firefox instances in build pipelines
- Process lifecycle control: manage Firefox startup, shutdown, and configuration injection programmatically
- Multi-instance testing: manage multiple concurrent Firefox processes with isolated profiles
- Browser compatibility testing: start different Firefox versions with consistent configuration

## Worth the install?

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

Mozrunner manages the lifecycle of Mozilla applications (Firefox, Thunderbird, etc.) — starting, stopping, and configuring them programmatically for testing and automation.

Yes, if you need to automate Mozilla application control in testing or CI/CD. Low install friction, active maintenance, no known vulnerabilities, and broad Python version support (3.8–3.13) make it a safe choice. The copyleft license is standard for Mozilla projects and poses no barrier to most use cases. Verify that your target Firefox/Thunderbird versions are compatible and that your deployment environment can support the package's Mozilla dependencies.

## Install

pip install mozrunner
uv add mozrunner
poetry add mozrunner

## Installing mozrunner

Before you install: Low friction to install; distributed as a pure-Python wheel. Actively maintained with recent release. Depends on six Mozilla packages (mozdevice, mozfile, mozinfo, mozlog, mozprocess, mozprofile) that handle complementary concerns.

License in practice: Licensed under Mozilla Public License 2.0 (copyleft). Derivative works and modifications must be released under MPL 2.0; proprietary use of unmodified binaries is permitted, but source changes require reciprocal licensing.

Quickstart:

pip install mozrunner

from mozrunner import FirefoxRunner
runner = FirefoxRunner()
runner.start()
runner.stop()

Requires Python 3.8 or later; target Mozilla application must be installed on the system.

Verify before relying:

- Whether mozrunner requires Firefox or other Mozilla applications to be pre-installed on the system
- Whether it supports headless browser operation or requires a display
- Specific version compatibility constraints with Firefox/Thunderbird versions

## Package facts

- License: MPL 2.0 (copyleft)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 246.3K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

firefox automation control, mozilla application launcher, browser process management, firefox start stop, mozilla testing framework, automated browser startup, firefox configuration automation, mozilla-automation, browser-control, testing-framework

[View on SkillFed](https://skillfed.io/packages/mozrunner) · [View on PyPI](https://pypi.org/project/mozrunner/)