Alt Tab: MRU Switcher

🚀 Firefox Alt-Tab: MRU Switcher

A powerful, privacy-first Firefox extension that brings the native Most Recently Used (MRU) tab switching experience (likened to Windows Alt+Tab or macOS Cmd+Tab) to your browser.

📖 Table of Contents

• Features
• Installation
• Usage (Keyboard Shortcuts)
• Customization
• How to Update Extension Icon
• Troubleshooting
• Privacy & Security
• Architecture & Development
• License

✨ Features

• MRU Switching: Cycle through tabs based on their last active time rather than their linear order in the tab bar.
• Event Page Context: Built using Manifest V3 for maximum performance and security.
• Zero-Latency Persistence: Maintains history state even when the background process is suspended by the browser.
• Privacy Core: No tracking, no data collection, and minimal permission requirements.

Since this extension is optimized for direct control and privacy, we recommend sideloading it using the temporary add-on feature:

1. Download the source: Clone this repository or download the ZIP file and extract it.
2. Open Debugging: Enter about:debugging#/runtime/this-firefox in your browser.
3. Load: Click Load Temporary Add-on… and select the manifest.json file from the extracted folder.

[!NOTE] Temporary add-ons are removed when Firefox is closed. For persistent installation, package the extension as an .xpi file and sign it via addons.mozilla.org (free, no fees ever).

[!TIP] You can remap these keys at about:addons → click the gear icon (⚙️) → Manage Extension Shortcuts.

How to Update Extension Icon

To brand or update the visual identity of your extension, follow these standard steps:

1. Image Preparation: Create a new icon image. Recommended dimensions are 128x128 pixels.
2. Replacement: Save your new icon as icon.png in the project root directory, overwriting the existing file.
3. Manifest Configuration: Ensure that manifest.json correctly points to your file. By default, it is configured as follows: json "icons": { "128": "icon.png" }, "action": { "default_icon": "icon.png" }
4. Apply Changes: Go to about:debugging#/runtime/this-firefox and click the Reload button on the extension card to refresh the assets.

If keyboard shortcuts are not responding:

1. Check for conflicts: Another extension or Firefox itself may have claimed the same shortcut. Go to about:addons → gear icon → Manage Extension Shortcuts to verify or reassign.
2. Reload the extension: Navigate to about:debugging#/runtime/this-firefox and click Reload on the extension entry.
3. Check the console: Click Inspect on the extension entry in about:debugging to open the extension's developer console for error messages.

🔒 Privacy & Security

This extension follows a Zero Host Permission policy. We ONLY request access to:

• tabs: To allow switching between IDs.
• storage: Only for browser.storage.session to maintain state across background script restarts.

We cannot read page content, track your browsing history, or exfiltrate any data.

💻 Architecture & Development

For a deep dive into the technical implementation, state reconciliation logic, and Manifest V3 specifics, please refer to our Developer Walkthrough (DEVELOPER.md).

📜 License

Distributed under the MIT License. See LICENSE for more information.