AI localization for Firefox add-ons
Upload your source messages.json, pick target languages, pay once, and download a ready-to-ship _locales ZIP.
How it works
Three simple steps to localize your Firefox add-on. Translations run after payment—we queue jobs and generate the ZIP in minutes.
Upload
Drop your source messages.json file. We parse it instantly and validate the Firefox add-on format.
Select languages & see price
Choose from 52 languages. See transparent pricing based on your file size before you pay.
Download ZIP
Pay once via Stripe. We generate all _locales/{lang}/messages.json files and bundle them into a ZIP.
Transparent pricing estimator
See exactly what you'll pay before uploading. Final quote is computed after upload based on string length and languages selected.
1. Upload file
Drop messages.json here
or click to browse
Firefox WebExtension format only. Max 500KB.
2. Select languages
3 of 55 languages selected
3. Your estimate
Final price calculated after file upload on checkout page
One-time payment • No subscription
Built for developers
Purpose-built for Firefox add-on locale format. Not a generic translation tool.
Firefox format aware
Built specifically for Firefox add-on messages.json structure with message, description, and placeholders support.
Placeholder protection
Preserves $PLACEHOLDER$ syntax exactly as-is. Your variables stay intact across all languages.
Description context
We read your description fields and use them as context hints for more accurate AI translations.
ZIP export ready
Download a ZIP with correct _locales/{lang}/messages.json folder structure. Drop it into your extension.
Parallel processing
All languages are translated simultaneously. Most jobs complete in under 5 minutes.
One-time payment
No subscriptions, no monthly fees. Pay once per job, download forever.
How Firefox extension i18n works
Firefox WebExtensions use the same messages.json format under _locales/. The "default_locale" field in manifest.json is required whenever the _locales/ directory exists — omitting it causes the add-on to be rejected. The browser.i18n API reads locale strings at runtime, with full support for $PLACEHOLDER$ substitution.
_locales/
├── en/
│ └── messages.json ← default_locale
├── de/
│ └── messages.json
├── fr/
│ └── messages.json
└── ja/
└── messages.json{
"appName": {
"message": "My Extension",
"description": "Extension name"
},
"greeting": {
"message": "Hello, $USER$!",
"placeholders": {
"user": { "content": "$1" }
}
}
}Runtime API
browser.i18nExample call
browser.i18n.getMessage("appName")Required in manifest
"default_locale"AMO (addons.mozilla.org) displays your add-on name and description in the reviewer's locale when _locales/ is present. Consistent translations across all locales improve store approval rates.
Why not just use generic tools?
General-purpose translation tools don't understand Firefox add-on format.
LocalePack | Manual translation | Generic TMS | |
|---|---|---|---|
| Setup time | 2 minutes | Hours per language | 30+ minutes |
| Cost transparency | |||
| Firefox format safety | |||
| Placeholder protection | |||
| Speed (52 languages) | < 5 min | Weeks | Hours |
| Best for | Firefox add-ons | Small projects | Enterprise web apps |
Trusted by extension developers
“Saved me hours of tedious work. Uploaded my messages.json, got back perfect translations in the exact format I needed.”
Sarah K.
Indie dev, AdBlock extension
“Finally a tool that understands Firefox add-on format. No more fixing broken placeholders after translation.”
Marcus T.
Extension maintainer
“Transparent pricing was the selling point. I knew exactly what I'd pay before uploading anything.”
Dev J.
Open source contributor
52
Locales supported
100%
Placeholder-safe output
ZIP
Ready to ship
Frequently asked questions
Everything you need to know about LocalePack.