firefox-addon

name	firefox-addon
description	Firefox add-on development, manifest validation, and AMO submission.
tagline	Firefox extension development and AMO submission
last-updated	"2026-06-06T00:00:00.000Z"

Firefox Add-on Development

This skill covers Manifest V3 Firefox extension development, including required manifest fields, AMO validation, and submission.

When to use

Use this skill when:

• Building or validating a Firefox extension manifest
• Submitting to Firefox Add-ons (AMO)
• Fixing AMO validation errors
• Configuring browser_specific_settings for Firefox

Required manifest fields

All new Firefox extensions must include data_collection_permissions in browser_specific_settings.gecko. This is validated on AMO submission.

For extensions that collect NO data (recommended for local/self-contained extensions):

{
  "browser_specific_settings": {
    "gecko": {
      "id": "your-extension@local",
      "data_collection_permissions": {
        "required": ["none"]
      }
    }
  }
}

This is appropriate when the extension:

• Stores data only in chrome.storage.local / browser.storage.local
• Makes API calls directly to user-specified endpoints
• Has no telemetry, analytics, or remote data transfer

For extensions that DO collect data:

{
  "data_collection_permissions": {
    "required": ["locationInfo", "browsingHistory", "..."],
    "optional": ["technicalAndInteraction", "..."]
  }
}

Available data types:

Required or optional:

• bookmarks, browsingHistory, cookies, credentialsOrAuth
• downloads, extensionDataAndConfig, geolocation
• locationInfo, personalCommunications, personalDataAndFiles, sensitiveInfo

Optional only (technicalAndInteraction cannot be required):

• technicalAndInteraction

AMO validation errors and fixes

Error	Fix
"data_collection_permissions" property is missing	Add field to browser_specific_settings.gecko
must have required property 'required'	Include "required": [...] array
"required" must be array	Use ["none"] or list of data types, not boolean/string
"data_collection_permissions" must be object	Use { "required": [...] }, not just []

AMO submission form requirements

When submitting to AMO, you'll need to complete several form sections:

1. Single purpose declaration

Confirm your extension has a single, narrow purpose. Be ready to explain it in ~1000 characters.

2. Permission justifications

For each permission in your manifest, provide a justification (max 1000 chars each):

• storage — explain what user settings/data you persist
• webNavigation — explain why you need to detect page navigation
• declarativeNetRequest — explain CORS/API call requirements
• host_permissions — explain which hosts you access and why

3. Source code submission

Mozilla requires source code for reviewed extensions:

• Submit a separate source zip (not the built extension)
• Include raw, untranspiled source files
• Include README.md or BUILD.md with step-by-step build instructions
• Include build script (e.g., build.mjs, package.json)
• List Node.js/npm version requirements
• Max file size: 200 MB

4. Screenshots

• PNG or JPG format
• Maximum size: 2400×1800 pixels
• At least one screenshot greatly increases install likelihood

Build and package workflow

1. Build the extension:

   npm run build
   

2. Package for submission (produces store-ready zip):

   npm run package
   

3. Prepare source package:

   # Include: src/, build script, package.json, README, manifests
   # Exclude: node_modules/, dist/, build output
   zip -r extension-source.zip src/ build.mjs package.json README.md manifest.firefox.json
   

4. Validate on AMO before submitting:

   • Go to AMO Developer Hub
   • Upload the built extension zip
   • Upload source zip when prompted
   • Fix any validation errors before final submission

Submission checklist

• data_collection_permissions field present in manifest
• Extension ID set in browser_specific_settings.gecko.id
• Screenshots ready (1280×800 or 2400×1800 max, PNG/JPG)
• Privacy policy URL (recommended)
• Source package prepared with build instructions
• Permission justifications written (max 1000 chars each)
• Single purpose description ready (~1000 chars)
• npm run package produces clean zip
• AMO validation passes with no errors/warnings

Differences from Chrome Web Store

Firefox AMO	Chrome Web Store
Requires data_collection_permissions	No equivalent field
Uses browser_specific_settings.gecko	Uses key for extension ID
Validates on upload	Validates during review
Requires source code submission	Source review on request
Auto-signs approved extensions	Requires manual review
No fee	$5 one-time developer fee
Screenshots: 2400×1800 max	Screenshots: 1280×800 or 640×400 exactly

References

• Firefox built-in consent for data collection
• Short link
• AMO Developer Hub
• Extension Workshop
• Source code submission requirements