Custom CSS Firefox

Custom CSS

Overwrite or inject custom CSS into website.

Features & Capabilities

Custom CSS is a straightforward Chrome extension designed for web developers and CSS enthusiasts. It empowers users to inject their own custom CSS into any website, allowing complete control over the site's appearance by overwriting default styles such as font size, font color, and other visual elements.

This extension enhances user experience by providing a flexible tool to personalize or test website styles dynamically without modifying the site's source code. Whether you want to improve readability, tweak design details, or experiment with styling, Custom CSS offers an easy and efficient solution to customize websites on the fly.

User Growth & Download Statistics

Manifest V2 Add-on Developer Tools Design
By:
Kenny Ooi
Daily users:
716 13
Rating:
4.17
(6)
Version:
1.1 Last updated: 2022-01-12
Version code:
5347695
Creation date:
2022-01-11
Risk:
High risk impact Low risk likelihood
Permissions:
Content scripts matches:
  • *
Size:
27.12KB
Email:
ke*****@qutebox.com
Full description:
See detailed description
Source:
Firefox Add-ons Store
Data ingested on:
2026-06-21
Compare stats and ranking:

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:
Kenny Ooi
Firefox Add-ons Store
https://addons.mozilla.org/firefox/addon/qb-custom-css/
Email:
ke*****@qutebox.com

User Reviews

by De*****, 2025-10-01

It is a lifesaver, a few css commands and YT is usable.
by wn*****, 2025-07-19

Awesome - this works reliably and does not spy on me like stylus and stylish do. I would love to see it expanded to manage styles by url in the future, that's why only four stars ;)
by ma*****, 2025-02-11
View all user reviews ›

Is Custom CSS 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.

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

Risk impact analysis details
  • Critical Grants access to browser tabs, which can be used to track user browsing habits and history, presenting a privacy concern.
  • Critical ****** ****** ** *** ********* ****** * *********** ******** **** ** ** *** ******* *** ****** **** **** *** ******* *****
  • High ******* ******* **** *** ****** ***** *** ***** ** ******* **** ********* ********* ** * *********** *****
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.

Custom CSS 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 **** ********* *** ***** **** **** * ****** **** ***** ********** *** **** ****** ** ** ****** *** *****
  • Good **** ********* *** **** **** *******
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Best Custom CSS Alternatives

Here are some Firefox add-ons that are similar to Custom CSS: