A browser extension is a small add-on that lives inside your browser and adds features the browser does not include by default. Extensions can block ads, manage passwords, check grammar, save articles, change page layouts, or add buttons and menus to websites.
Does this affect you?
Use this for Chrome, Firefox, Edge, and Safari on Windows or Mac when deciding whether to install an extension or remove ones you no longer use.
How an extension actually works
Extensions are usually built with the same web technologies websites use, which is why they can interact directly with pages.
- What it is built from: many extensions use HTML, CSS, and JavaScript. That lets them add interface elements, read page content, and modify pages when allowed.
- Where it comes from: install extensions from official stores such as the Chrome Web Store, Firefox Add-ons, Microsoft Edge Add-ons, or Safari extensions in the Mac App Store.
- What it can see: permissions explain what an extension can access. A broad permission such as read and change all your data on websites you visit can mean the extension may see page contents while active.
- When it runs: some extensions run only on matching sites, while others, such as content blockers, run on most or all pages.
How to tell a trustworthy extension from a risky one
A quick review before installing can prevent many problems.
- Check install count and ratings. Widely used extensions with solid reviews have usually had more scrutiny than brand-new extensions.
- Read the permissions. A simple tool asking for access to every website is worth questioning.
- Check the publisher. Prefer the official company or developer associated with the product, not a lookalike name.
- Remove what you do not use. Every extension is extra code in your browser and extra potential exposure.
More control
Broad permissions can be sensitive
A malicious or compromised extension with access to page contents may see information typed into forms or shown on pages. That can be risky even when the websites themselves are legitimate.
Good extensions can change ownership
There have been cases where trusted extensions were sold and later updated with ads, data collection, or other unwanted behavior. Review installed extensions periodically, not only when installing.
Official stores reduce risk but do not remove it
Browser stores use automated and sometimes manual review, but bad extensions have still slipped through. Treat store approval as one signal, not a guarantee.
Sources
- Google Chrome Help – Manage extensions in Chrome (2025)
- Mozilla Support – Find and install add-ons to add features to Firefox (2025)
- Apple Support – Use extensions in Safari on Mac (2025)