Browser Extension Safety — What Permissions to Watch For 2026

Browser extensions can read everything you type, see every website you visit, and steal your passwords. This guide explains how to audit extension permissions and stay safe. Updated March 2026.

Why Browser Extensions Are Dangerous

Browser extensions run inside your browser with elevated privileges. A malicious or compromised extension can read your passwords as you type them, steal banking session cookies, inject ads into every page, redirect your searches, and exfiltrate your browsing history. In 2026 alone, multiple popular extensions with millions of users were found to be secretly collecting and selling browsing data. The risk is real and underestimated by most users.

Dangerous Permissions to Watch For

When you install an extension, it requests permissions. Here are the most dangerous ones:

1. "Read and change all your data on all websites" — This is the most dangerous permission. It gives the extension full access to every website you visit, including banking sites, email, and social media. Only grant this to extensions you absolutely trust and need.
2. "Read and change your browsing history" — The extension can see every site you have ever visited and delete or modify history entries.
3. "Manage your downloads" — Can download files to your computer without your knowledge. Malware delivery vector.
4. "Modify data you copy and paste" — Can intercept clipboard content. Crypto address swapping attacks use this to replace wallet addresses.
5. "Read and modify cookies" — Can steal session cookies to hijack your logged-in accounts without needing your password.
6. "Communicate with cooperating native applications" — Can execute programs on your computer outside the browser sandbox.
7. "Change your privacy-related settings" — Can disable security features, change your proxy settings, or modify DNS.

How to Audit Your Extensions

Chrome

1. Go to chrome://extensions
2. Click "Details" on each extension to see its permissions
3. Click "Site access" to control which sites the extension can access
4. Remove any extension you do not actively use — dormant extensions are still a risk
5. Set extensions to "On click" instead of "On all sites" where possible

Firefox

1. Go to about:addons
2. Click on each extension and review "Permissions"
3. Firefox shows permissions more clearly than Chrome and requires explicit consent for each
4. Firefox extensions are reviewed by Mozilla staff before listing — but this is not foolproof

Chrome vs Firefox Permission Models

Chrome uses Manifest V3, which limits background scripts and restricts some powerful APIs. However, Chrome still allows broad "all sites" access. Google reviews extensions algorithmically, which means some malicious ones slip through. Firefox uses a more granular permission model and has human reviewers for listed extensions. Firefox also supports container tabs that isolate extension access per tab, adding an extra layer of security. For privacy-conscious users, Firefox generally offers better extension security controls.

Safe Extension Practices

• Minimize extensions: Every extension is an attack surface. Only install what you truly need.
• Check the publisher: Is the developer a known company or individual? Check their website and reputation.
• Read recent reviews: Look for reviews mentioning unexpected behavior, ads, or slowness. A previously safe extension can go rogue after being sold to a new owner.
• Check update frequency: Extensions that haven't been updated in over a year may be abandoned and vulnerable.
• Use open source extensions: Extensions with public source code (e.g., uBlock Origin, Bitwarden) can be verified by the community.
• Watch for ownership changes: Popular extensions are sometimes bought by companies that inject ads or tracking. If an extension suddenly asks for new permissions after an update, investigate before accepting.

Recommended Safe Extensions

• uBlock Origin — Open source ad/tracker blocker. Does not "accept acceptable ads." Lightweight.
• Bitwarden — Open source password manager extension. Audited. Cross-platform.
• HTTPS Everywhere — Forces HTTPS connections (now largely built into browsers).
• Privacy Badger — EFF's tracker blocker. Learns tracking behavior automatically.

Check any extension's trust score at nerq.ai/extensions.

Related Guides

Updated March 2026. Source: Nerq independent analysis.