# CSS Sentry

> CSS Sentry detects and reduces risk from CSS-based data exfiltration techniques. It analyzes page styles for suspicious selector probing, remote CSS resource sinks, imports, SVG/CSS resource behavior, and rendered-content CSS injection patterns.

Canonical page: [https://chrome-stats.com/d/css-sentry?hl=es](https://chrome-stats.com/d/css-sentry?hl=es)

## Overview

- **ID:** `css-sentry`
- **Platform:** Firefox
- **Type:** Firefox add-on
- **Status:** Available
- **Publisher:** dougg0k
- **Category:** other
- **Daily users:** 2
- **Version:** 1.0.110
- **Last updated:** 2026-06-19
- **First published:** 2026-04-29
- **Size:** 271 KB
- **Data as of:** 2026-09-11
- **Store listing:** [Firefox Add-ons Store](https://addons.mozilla.org/firefox/addon/css-sentry/)
- **Website:** [https://github.com/dougg0k/css-sentry](https://github.com/dougg0k/css-sentry)

## Description

CSS Sentry is a local-only browser extension that helps detect and reduce risk from CSS-based data exfiltration techniques. It analyzes page styles for suspicious selector probing, remote CSS resource sinks, CSS imports, SVG/CSS resource behavior, data stylesheets, and rendered-content CSS injection patterns.

The extension is designed as a defense-in-depth tool. It includes Passive, Balanced, and Strict protection modes, local reports, destination allow/block policy support, advanced compatibility options, and optional Firefox-specific enhanced stylesheet inspection.

CSS Sentry does not use telemetry, cloud analysis, or a remote service. Reports are stored locally in your browser.

This extension does not claim to prevent every CSS side channel, browser bug, sanitizer bypass, or future CSS feature. It is intended to reduce exposure to known high-signal CSS exfiltration patterns while minimizing normal browsing breakage.

## Rankings

- #63,506 — Overall
- #18 — data entry

## Permissions and access

### Permissions

- `storage`
- `declarativeNetRequest`
- `webNavigation`
- `webRequest`
- `webRequestBlocking`
- `<all_urls>`

### Content script matches

- `<all_urls>`

## Safety

- **Risk impact:** High risk impact
- **Risk likelihood:** High risk likelihood

### Analysis details

- Allows access to all websites, posing a significant security risk as it can monitor and modify data from any visited site.
- This extension has low user count. Unpopular extensions may not be stable or safe.

> Some risk analysis details are omitted from this free response. [Upgrade to view the full analysis](https://chrome-stats.com/pricing).

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Source: [Chrome-Stats](https://chrome-stats.com/d/css-sentry?hl=es)