Senior Software Engineer, WebExtensions

Mozilla

Software Engineer on Mozilla's WebExtensions team implementing new features and supporting extension developers. Collaborating with teams to ensure safety and performance in Firefox extensions.

Posted 5/13/2026full-timeRemote • 🇺🇸 United StatesSeniorWebsite

Tech Stack

Tools & technologies

AndroidJavaScriptOpen SourceRust

About the role

Key responsibilities & impact

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

Requirements

What you’ll need

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

Benefits

Comp & perks

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)

ATS Keywords

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Hard Skills & Tools

JavaScriptDOM APIsHTMLCSSAPI designAPI integrationC++Rustweb security principlesbrowser architecture

Soft Skills

strong communication skillscollaborationproblem-solvingdiagnosing issuesdocumentation improvement