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Mozilla

Contract Staff Software Engineer-Bug Burndown

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Remote from
Germany
Salary
Undisclosed
Department
Software Engineering
Employment
Contract
Experience
Senior
Published
Apply before
20 Nov 2026
Listing views
16
Application actions
1
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AI Summary

The role, at a glance.

Mozilla is seeking a contract software engineer to reduce Firefox’s long-tail WebCompat backlog. The work centers on reproducing site-breakage reports, validating diagnoses, and turning issues into actionable bugs, interventions, or simple landed fixes. Strong practical HTML, CSS, JavaScript, browser developer-tools, and cross-browser debugging skills are essential. The engineer will use AI tooling to accelerate investigation and implementation, while Gecko and web-standards experience are advantageous. This is a focused engineering role requiring disciplined triage and clear technical documentation.

Role DNA

A quick view of the complexity, pace, ownership and collaboration implied by the job description.

Job Complexity

4/5
EasyHard

Pace & Pressure

4/5
RelaxedFast-paced

Autonomy Level

4/5
GuidedFull ownership

Communication Load

3/5
IndependentCollaborative
AI insightDiagnosing real-world browser compatibility failures requires careful reproduction, root-cause isolation, and knowledge of differing browser behavior. The long-tail backlog and expectation to land fixes create a sustained, delivery-oriented workload.

Salary analysis

Estimated compensation compared with the broader US market for similar roles.

Estimated job median (per year)Highly competitive
$150,000
US market range (per year)$120k–$180k
AI insightThe yearly pay period is inferred from the job context; it was not explicitly stated by the employer. No employer compensation is disclosed. The yearly cadence and USD market estimate are inferred for a senior contract-oriented web compatibility engineering role; actual contract compensation may vary by engagement structure and German hiring arrangement.

Core skills

Skills and capabilities most closely associated with this opportunity.

JavaScriptHTMLCSSWeb compatibilityCross-browser debuggingBrowser DevToolsBug triageFirefoxGeckoWeb standardsAI-assisted developmentIssue diagnosisSoftware testingTechnical documentation
Sample interview questions
How would you investigate a report that a website works in one browser but breaks in Firefox?

I would first reproduce the issue in a clean Firefox profile and compare behavior with the working browser. I would inspect console errors, network requests, DOM structure, CSS layout, and feature support, then narrow the issue to site code, browser behavior, or an extension/intervention opportunity. I would document reliable reproduction steps and the evidence supporting the diagnosis.

What makes a WebCompat intervention appropriate instead of changing browser code?

An intervention is appropriate when a narrowly scoped site workaround can safely address an incompatibility without changing standards-compliant browser behavior broadly. I would assess user impact, risk of regressions, maintainability, and whether the site is likely to fix its own code before selecting that route.

How do you use AI tools while debugging production web issues?

I use AI tools to accelerate hypothesis generation, interpret unfamiliar code, draft test cases, and propose small patches. I validate every suggestion by reproducing the behavior, reviewing the generated code, checking browser compatibility, and running targeted tests rather than treating AI output as authoritative.

Describe your process for triaging a large backlog of bug reports.

I group reports by reproducibility, user impact, duplicates, likely root cause, and estimated effort. I prioritize issues that are actionable and high-impact, close incomplete diagnoses with clear evidence, and keep each ticket updated with concise reproduction steps, findings, and recommended next actions.

What would you check when a CSS issue appears only in Firefox?

I would compare computed styles, layout metrics, rendering behavior, CSS parsing, and feature support across browsers. I would reduce the problem to a minimal test case, consult relevant specifications and known browser behavior, and determine whether the cause is invalid site CSS, a compatibility difference, or a potential Firefox defect.

This analysis is generated from the job description. Salary estimates, role characteristics and sample answers are guidance, not employer-provided facts.
Opportunity details

About this role.

You will help reduce Firefox’s WebCompat bug backlog by finishing or verifying the diagnosis of the long tail of site-breakage bugs, and by writing interventions or simple fixes (often with AI assistance). You turn a large queue of reported breakages into diagnosed, actionable, or fixed bugs.

Responsibilities

  • Finish diagnosing, or verify the diagnosis of, long-tail WebCompat bugs.
  • Write WebCompat interventions where appropriate.
  • Write simple fixes (AI-assisted) and land them.
  • Reproduce and triage incoming site-breakage reports.

Required qualifications

  • Solid web development (HTML, CSS, JavaScript) and comfort debugging real-world site breakage.
  • Fluent with browser devtools and cross-browser diagnosis.
  • Comfortable using AI tooling to speed up diagnosis and fixes.

Preferred

  • Gecko knowledge is a strong plus (but can be taught).
  • Prior WebCompat or web-standards experience.

Apply now >

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