CSS Sentry

Name: CSS Sentry
Author: dougg0k

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.

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Features & Capabilities

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.

User Growth & Download Statistics

Add-on

By:

dougg0k

Daily users:

Version:

1.0.107 Last updated: 2026-05-17

Version code:

6266103

Creation date:

2026-04-29

Risk:

Permissions:

Content scripts matches:

<all_urls>

Size:

272.21KB

URLs:

Website

Full description:

Source:

Firefox Add-ons Store

Data ingested on:

2026-06-04

Compare stats and ranking:

Ranking

# 111,288 ▲ 494

Other rankings

#21 in data entry keyword 28

For Developers

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Contact the developer

Chrome-Stats does not own this Firefox add-on. Please use these information below to contact the Firefox add-on developer.

Developed by:

dougg0k

Firefox Add-ons Store

https://addons.mozilla.org/firefox/addon/css-sentry/

Website:

https://github.com/dougg0k/css-sentry

Permission Change History

2026-05-14: Version 1.0.34 → 1.0.59

Add Permissions: webRequestBlocking

Is CSS Sentry Safe?

Risk impact

Risk impact measures the level of extra permissions an extension has access to. A low risk impact extension cannot do much harms, whereas a high risk impact extension can do a lot of damage like stealing your password, bypassing your security settings, and accessing your personal data. High risk impact extensions are not necessarily malicious. However, if they do turn malicious, they can be very harmful.

CSS Sentry requires some sensitive permissions that could impact your browser and data security. Exercise caution before installing.

Risk impact analysis details

Critical Allows access to all websites, posing a significant security risk as it can monitor and modify data from any visited site.
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Risk likelihood

Risk likelihood measures the probability that a Firefox add-on may turn malicious. This is determined by the publisher and the Firefox add-on reputation on Firefox Add-ons Store, the amount of time the Firefox add-on has been around, and other signals about the Firefox add-on. Our algorithms are not perfect, and are subject to change as we discover new ways to detect malicious extensions. We recommend that you always exercise caution when installing a Firefox add-on.

CSS Sentry is recently added, and hasn't been around long enough for us to gather enough data to accurately assess its risk level.

Risk likelihood analysis details

High This extension was recently updated in the past month. New updates may not be stable or safe.
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