Objective: Use this skill to reduce CSP-violation rejections, manifest-schema breakages, AMO-review failures, and cross-browser compat bugs by enforcing manifest-version discipline, CSP-safe patterns, and web-ext-verification rules below.

Firefox WebExtension Development

Core Rules (do X because Y)

• Use browser namespace because it is Promise-based natively in Firefox, avoiding callback boilerplate.
• Pin manifest_version: 3 for new extensions because MV2 is sunsetting and AMO warns on new MV2 submissions.
• Always include browser_specific_settings.gecko.id because AMO rejects extensions without a unique ID.
• Set strict_min_version: "109.0" for MV3 because service workers and the action API require Firefox 109+.
• Use web-ext run --profile-create-new for testing because stale profile state causes false positives.

See references/apis.md for the complete WebExtension API namespace list (51 APIs) and usage patterns.

Manifest V3 Rules

See references/manifest-v3.md for the full MV3 manifest schema reference.

MV2 vs MV3 Migration Rules