fhosts by Amal Graafstra

fhosts lets you override hostname-to-IP resolution for any domain, directly in Firefox, on a per-tab basis. Perfect for staging or local web development when you need to test with production hostnames.

Why use fhosts?

When developing, you often need production hostnames to work correctly - for cookies, CORS policies, OAuth callbacks, or SSL certificates. Instead of editing your system hosts file (which affects your entire computer), fhosts lets you:

• Map any hostname to any IP address (e.g., myapp.com → 127.0.0.1)
• Enable overrides per-tab - test local and production side-by-side
• Keep your system hosts file clean

How it works

1. Add hostname mappings (e.g., example.com → 127.0.0.1)
2. Click the toggle to enable overrides for the current tab
3. Navigate to your mapped domain - requests route to your specified IP

The toolbar icon turns cyan when overrides are active for the active tab.

Requirements

This extension requires a companion proxy helper to perform the actual IP substitution. Download the installer from the GitHub releases page: https://github.com/amalg/fhosts/releases

HTTPS Note

When accessing HTTPS sites, you'll see certificate warnings since the certificate won't match the IP. For local development, use tools like mkcert for local SSL certificates.

Open Source

fhosts is open source under the MIT license. View the code, report issues, or contribute at: https://github.com/amalg/fhosts