CustomCSS Injector

Name: CustomCSS Injector
Rating: 4.2727 (22 reviews)
Author: Blizz3

By: Blizz3

- Apply any CSS rules for any websites, including iframes. - Whitelist and Blacklist functionality - Apply CSS rules to specific URLs, Domains or Globally - Syntax highlighting & line numbers - Update without page refresh

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Features & Capabilities

CustomCSS Injector is a powerful Chrome extension enabling users to inject custom CSS rules on any website effortlessly. Customize colors, backgrounds, hide elements, and more—all without refreshing the page. Control where your CSS applies using whitelist and blacklist features, targeting specific URLs, entire domains, or applying styles globally.

With built-in syntax highlighting and line numbers powered by PrismJS, editing your styles becomes clear and user-friendly. Whether you want to personalize your browsing experience or override web page styles, CustomCSS Injector offers an easy and flexible solution for CSS injection.

User Growth & Download Statistics

Add-on Developer Tools Design

By:

Blizz3

Daily users:

911 16

Rating:

4.27

(22)

Version:

1.3.2 Last updated: 2020-04-02

Version code:

4995480

Creation date:

2019-07-06

Risk:

Permissions:

Content scripts matches:

<all_urls>

Size:

43.28KB

Email:

br*****@gmail.com

URLs:

Website

Full description:

Source:

Firefox Add-ons Store

Data ingested on:

2026-06-15

Compare stats and ranking:

Ranking

# 3,455 ▲ 18

Other rankings

#193 in Feeds, News & Blogging ▲ 2

#8 in inject keyword 14 ▲ 1

#31 in custom feed keyword 21

#32 in custom font keyword 29

#43 in rule keyword 8

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For Developers

Monetize with App Pass Boost with Extension Booster

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:

Blizz3

Firefox Add-ons Store

https://addons.mozilla.org/firefox/addon/customcss-injector/

Email:

br*****@gmail.com

Website:

https://github.com/blizz31/customcssinjector/

User Reviews

Overall, reviewers find CustomCSS Injector powerful, easy to use, and lightweight with strong multi-scope CSS override capabilities, and effective for practical page tweaks. However, reliability issues with domain-level CSS, the need to save changes before leaving the editor, late injection timing, occasional bugs, and requests for export/import/list features temper enthusiasm. The add-on is valuable but could use stability and UX improvements.

Pros

Powerful and easy to use for CSS overrides across sites.
Lightweight and unobtrusive.
Editor supports syntax highlighting.
Works across multiple scope levels (Global, URL, Domain).
Practical usefulness for fixing problematic pages and customizing experiences (overriding CSS on tricky sites).

Cons

Reliability issues with domain-level CSS: sometimes not applied, requires refresh, or can mix across domains.
Unsaved changes can be lost if you don't click Save before leaving the editor.
CSS injection can occur after the page has loaded, limiting early rendering changes.
Occasional bugs or lack of feedback (initially shows errors or red highlight).
Missing export/import or domain/list view feature for managing multiple CSS rules.

Recent reviews

Save button doesn't work for me.

by *****, 2026-03-31

by Pi*****, 2026-02-20

Very good, but it would be nice if there was a way to see a list of the domains/URLs we have custom CSS for, as well as being able to export/import.

by Mo*****, 2026-01-02

View all user reviews ›

Is CustomCSS Injector 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.

CustomCSS Injector requires a few sensitive permissions. 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.

CustomCSS Injector has earned a fairly good reputation and likely can be trusted.

Risk likelihood analysis details

High This extension has low user count. Unpopular extensions may not be stable or safe.
Low **** ********* *** ******* **** **** * ****** **** ***** ******** *** **** ****** ** ** ****** *** *****
Low **** ********* *** ***** **** **** * ****** **** ***** ********** *** **** ****** ** ** ****** *** *****
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