# CustomCSS Injector

> - 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

Canonical page: [https://chrome-stats.com/d/customcss-injector](https://chrome-stats.com/d/customcss-injector)

## Overview

- **ID:** `customcss-injector`
- **Platform:** Firefox
- **Type:** Firefox add-on
- **Status:** Available
- **Publisher:** Blizz3
- **Category:** feeds-news-blogging,web-development,appearance,social-communication
- **Daily users:** 818
- **Weekly downloads:** 17
- **Rating:** 4.27 / 5 (22 ratings)
- **Version:** 1.3.2
- **Last updated:** 2020-04-02
- **First published:** 2019-07-06
- **Size:** 43 KB
- **Data as of:** 2026-09-04
- **Store listing:** [Firefox Add-ons Store](https://addons.mozilla.org/firefox/addon/customcss-injector/)
- **Website:** [https://github.com/blizz31/customcssinjector/](https://github.com/blizz31/customcssinjector/)

## Description

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.

## Rankings

- #3,677 — Overall
- #208 — Feeds, News & Blogging
- #8 — inject
- #33 — custom feed
- #34 — custom font
- #50 — rule

## Permissions and access

### Permissions

- `storage`
- `<all_urls>`
- `contextMenus`
- `notifications`

### Content script matches

- `<all_urls>`

## Safety

- **Risk impact:** Moderate risk impact
- **Risk likelihood:** Low 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).

## Review summary

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.

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Source: [Chrome-Stats](https://chrome-stats.com/d/customcss-injector)