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MCMozilla Corporation
Mozilla CorporationWeb Browser

Senior Software Engineer, WebExtensions

Location

Remote, France

Work type

Remote

Employment

Full Time

Experience

4-8 years

Compensation

Compensation not disclosed

Posted

2d ago

Summary and responsibilities

Role overview

Summary

As a Senior Software Engineer, WebExtensions, you will be responsible for implementing and maintaining WebExtensions APIs and Addon Management within the Firefox browser. This role involves debugging issues, collaborating with various teams, and contributing to open-source workflows to ensure a safe, powerful, and reliable extension ecosystem for millions of users.

About this team and role:

The WebExtensions platform powers the add-ons ecosystem in Firefox, enabling millions of users to customize their browser while keeping safety and performance at the forefront. As a WebExtensions Engineer, you will help implement new extension capabilities, improve existing APIs, and ensure that extensions remain reliable across Firefox.

As a Software Engineer on the WebExtensions team, you’ll bring a passion for exploring complex systems and creating experiences that balance developer power with user trust. You’ll work deep in the Gecko platform to evolve extension capabilities, and you’ll build UI features in Firefox that make extensions clear and manageable for users. Along the way, you’ll collaborate with experts across Mozilla and help advance cross-browser compatibility and the path toward standardization. Your work will keep extensions safe, powerful, and reliable for developers and millions of Firefox users.

What you’ll do:

  • Implement and maintain WebExtensions APIs and Addon Management, balancing power, safety, and performance, as well as user interfaces in Firefox.

  • Debug and fix issues affecting extensions in Firefox.

  • Collaborate with product managers, QA, and the AMO engineering team to deliver features end-to-end.

  • Contribute to Mozilla-owned extensions and system add-ons.

  • Participate in open source workflows: code reviews, pull requests, and discussions in Bugzilla/GitHub.

  • Support extension developers by helping diagnose issues and improving tooling/documentation.

What you’ll bring:

  • 4+ years of professional experience in software development.

  • Strong proficiency in JavaScript, DOM APIs, HTML, and CSS.

  • Familiarity with modern browser architecture and debugging tools.

  • Experience with API design and integration.

  • Ability to navigate and learn from large codebases.

  • Strong communication skills and experience collaborating in distributed teams.

Bonus points for:

  • Experience with Firefox internals, C++ or Rust.

  • Familiarity with Android or GeckoView development.

  • Knowledge of web security principles.

  • Contributions to open source projects, especially in browser or extension development.

What you’ll get:

  • Generous performance-based bonus plans to all eligible employees - we share in our success as one team

  • Rich medical, dental, and vision coverage

  • Generous retirement contributions with 100% immediate vesting (regardless of whether you contribute)

  • Quarterly all-company wellness days where everyone takes a pause together

  • Country specific holidays plus a day off for your birthday

  • One-time home office stipend

  • Annual professional development budget

  • Quarterly well-being stipend

  • Considerable paid parental leave

  • Employee referral bonus program

  • Other benefits (life/AD&D, disability, EAP, etc. - varies by country)

Updated 2d ago

Candidate fit

Skills and qualifications

Additional skills

JavaScript • 1+ yrs
DOM APIs • 1+ yrs
HTML • 1+ yrs
CSS • 1+ yrs
API design • 1+ yrs
API integration • 1+ yrs
Debugging • 1+ yrs
Collaboration • 1+ yrs
Communication • 1+ yrs
Firefox internals • 1+ yrs
C++ • 1+ yrs
Rust • 1+ yrs
Android development • 1+ yrs
GeckoView development • 1+ yrs
Web security principles • 1+ yrs
Open source contributions • 1+ yrs

Experience

4-8 years

How this role is positioned

Role classification

Job domains

Software Engineering

Industries

Technology & IT

Employment

Full Time

Contract duration

Permanent

Hiring type

Direct

Global hiring

Location specific

Offer details

Compensation and benefits

Compensation

Compensation not disclosed

VisibilityShared on listing
CurrencyUSD
PeriodYearly

Benefits and perks

Paid Parental Leave
Employee Referral Bonus

Location, schedule, and role shape

Work setup

Work conditions

Primary locationRemote, France
Work typeRemote
Global hiringNo

Bandwidth profile

peopleHigh8/10
physicalLow1/10
cognitiveHigh8/10
executionHigh8/10
creativityMedium6/10
uncertaintyMedium6/10
communicationHigh8/10

Context on the employer

Company snapshot

Company

Mozilla Corporation

Team size

Growing team

Location

Remote, France

Mozilla Corporation is the non-profit-backed technology company that has shaped the internet for the better over the last 25 years. We make pioneering brands like Firefox, the privacy-minded web browser. Now, with more than 225 million people around the world using our products each month, we’re shaping the next 25 years of technology and helping to reclaim an internet built for people, not companies. Our work focuses on diverse areas including AI, social media, security and more. And we’re doing this while never losing our focus on our core mission – to make the internet better for people. The Mozilla Corporation is wholly owned by the non-profit 501(c) Mozilla Foundation. This means we aren’t beholden to any shareholders — only to our mission. Along with thousands of volunteer contributors and collaborators all over the world, Mozillians design, build and distribute open-source software that enables people to enjoy the internet on their terms.

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Senior Software Engineer, WebExtensions

Remote, FranceFull Time