Specter

Keep tabs looking active when you switch away.

Specter is an open-source browser extension that keeps supported tabs looking active when you switch away. It controls page visibility and focus APIs, supports per-site exceptions, and stores optional activity logs locally.

The interface pairs a uBlock Origin-style layout (a popup with one power button and a tabbed dashboard) with a T3 Code-inspired skin and motion, in light, dark, and system themes. Advanced exposes injection, timing, diagnostics, and synthetic activity controls.

Features

• Global and per-tab protection controls
• Time-limited or permanent site exceptions
• Optional local event log and site activity view
• Configurable focus-event handling, reload behavior, synthetic activity, and decoy timing
• JSON settings backup and restore, plus JSON/CSV event export
• Keyboard shortcuts for global and active-tab controls
• Local fonts, icons, and assets with no runtime CDN dependency

Privacy

Specter has no analytics, advertising, accounts, or remote service. Settings, exceptions, and optional logs remain in browser extension storage. See PRIVACY.md for the full data-handling statement.

Extension coexistence

Specter's page hooks run in the website's main JavaScript world. Its settings bridge and other browser extensions run in isolated extension worlds, so Specter does not replace their JavaScript APIs. Blocked page listeners are gated individually; Specter does not stop native event propagation.

This design allows browser-assistance extensions, including the ChatGPT browser-control extension, to operate alongside Specter. Browser security boundaries still apply: Specter never injects into chrome-extension: or moz-extension: pages, browser-internal pages, or other protected surfaces.

The Diagnostics page shows the shortcuts actually assigned by the browser. If a browser leaves a command unassigned because another extension already uses that key combination, Specter links directly to the browser's shortcut manager so the binding can be changed without altering protection behavior.

Fresh installs use Ctrl+Shift+K (Command+Shift+K on macOS) for global protection and Alt+Shift+L for the current tab. Existing browser-specific assignments are preserved and can be changed from the shortcut manager.

Install for development

Ready-built archives are available from GitHub Releases. For Chrome, extract specter-chrome.zip and load the extracted folder containing manifest.json. For Firefox-family browsers, load specter-firefox.zip as a temporary add-on using the steps below. The Firefox archive is unsigned and is not a permanent signed-store installation.

Chromium browsers

1. Download or clone this repository.
2. Open chrome://extensions (or the equivalent extensions page).
3. Enable Developer mode.
4. Choose Load unpacked and select the repository folder.

Firefox-family browsers

Specter supports desktop Firefox and maintained Gecko-based derivatives that implement compatible Manifest V3 WebExtensions, including current LibreWolf, Floorp, and Zen Browser releases when the browser permits user-installed extensions.

1. Run npm run build to create the Firefox-family packages.
2. Open about:debugging#/runtime/this-firefox (or the derivative's equivalent page).
3. Choose Load Temporary Add-on.
4. Select specter-firefox.zip. The supported Firefox-family package requires Gecko 152 or later.

Temporary installations are removed when the browser closes. Browsers that enforce Mozilla extension signing require a signed distribution build for permanent installation. Vendor restrictions, protected internal pages, and Tor Browser security policy still apply.

Permissions

Permission	Why Specter needs it
storage	Saves settings, site exceptions, and optional local logs.
tabs	Reads the active tab and applies per-tab protection state.
scripting	Injects the main-world script required to control page visibility and focus APIs.
<all_urls>	Makes protection available on supported web pages. Browser-internal and restricted pages remain unavailable.

Development

The core build and unit suite have no package dependencies. Node.js and Python 3 are required for validation and release archives. The optional node tests/browser-ui.cjs integration suite needs Playwright and its Chromium binary in the development environment. Set SPECTER_LIVE_CODEPEN=1 to include the external regression page.

npm test
npm run build

npm test validates manifest references and licenses, checks HTML and JavaScript, exercises core protection policy, and verifies deterministic target-specific archives. npm run build additionally creates specter-chrome.zip and specter-firefox.zip from extension runtime files only.

The automated suite includes a coexistence regression that models an isolated extension observer and verifies that it continues receiving lifecycle events while Specter gates the corresponding page listener.

The manual behavior suite is available at tests/test-suite.html. Load the unpacked extension first, enable file URL access, then open the suite in a supported browser.

Project layout

background.js          Service worker, settings, policy, and messaging
content.js             Isolated-world bridge and page lifecycle handling
injected/              Main-world visibility and focus overrides
popup/                 Fast active-tab controls
options/               Full settings application
styles/                Shared tokens, typography, theme, and controls
tests/                 Manual browser behavior suite
scripts/               Validation and release packaging

Release process

1. Update manifest.json, package.json, and CHANGELOG.md to the same version.
2. Run npm run build.
3. Review the generated archives locally.
4. Merge the release PR into main.
5. Push a matching tag such as v1.0.0. The release workflow creates a GitHub release with both archives.

Limitations

• Browser-internal pages and extension stores block content-script injection.
• Websites can use signals outside the visibility and focus APIs Specter controls.
• Extension behavior may conflict with a site's terms or expected operation; users are responsible for where they enable it.
• Headless Chromium commonly disables Manifest V3 extensions.

Contributing and security

Read CONTRIBUTING.md before opening a pull request. Report suspected vulnerabilities privately as described in SECURITY.md.

Specter is licensed under the MIT License.