Why You Might Want to Install a Firefox Temporary Extension

Temporary extension installation is essential when you’re actively developing a Firefox add-on or conducting a round of testing before submitting it to Mozilla Add-ons (AMO). Unlike permanent installations, temporary installations don’t require packaging and signing for each iteration, which saves a ton of time during development.

• Fast testing: No need to repackage or sign each version.
• Efficient debugging: Use Firefox Developer Tools directly on the installed extension.
• Real-world simulation: See how the extension performs in the actual browser environment.

Pre-installation Requirements

• Latest version of Firefox or Firefox Developer Edition.
• A valid .xpi extension file or unpacked directory containing your extension.
• Basic understanding of manifest.json and WebExtensions (recommended).

Two Methods to Install a Temporary Extension in Firefox

Method 1: Drag-and-Drop the .xpi File

1. Open Firefox.
2. Type about:debugging into the address bar and hit Enter.
3. Click “This Firefox” from the left menu (or “This Nightly” in Developer Edition).
4. Locate your .xpi file in your file explorer.
5. Drag the .xpi file directly into the Firefox window.
6. Click “Add” when prompted to confirm the temporary installation.

Method 2: Load Unpacked Extension

1. Again, navigate to about:debugging > “This Firefox”.
2. Click “Load Temporary Add-on…”
3. Navigate to your extension folder and select either the manifest.json file or the entire directory.
4. The extension will now be temporarily loaded and appear in the Add-ons list.

What Happens After Installation?

Once installed, the extension remains active until you close Firefox. When you relaunch the browser, you’ll need to reinstall the extension using the same steps. This ensures a clean development cycle every time.

Tips for Testing and Debugging

• Use browser console (Ctrl+Shift+J) for logging and debugging output.
• Click on the “Inspect” button next to your loaded add-on for a full-featured debugger.
• Ensure manifest.json has all required fields like manifest_version, name, and version.

Common Errors and Fixes

• Error: Manifest file missing or unreadable – Make sure you’re selecting the correct file or directory.
• Error: Extension is unsigned – This doesn’t apply to temporary installs. Avoid trying to load it from about:addons.
• Error: Extension doesn’t appear – Refresh the debugging page and try again, or check your file structure.

Related Links

• MDN: Temporary Installation in Firefox
• Firefox Extension Workshop Guide

FAQs