How to Audit Browser Extension Permissions Before They Get Hijacked

Last month, a colleague of mine lost two days of work because a Chrome extension she'd installed years ago — a simple PDF converter — pushed an update that silently injected affiliate links into every shopping page she visited. The extension hadn't changed hands openly. The original developer had quietly sold it, and the new owner had baked in a script that abused the "<all_urls>" host permission she'd granted back in 2021 without a second thought.

This is more common than most people realize. A 2023 analysis of the Chrome Web Store by security researchers found that hundreds of extensions with millions of combined installs requested permissions far beyond what their stated function required. Extensions get abandoned, sold, or compromised, and the permissions you approved on day one keep working on day one thousand. The browser doesn't ask again. It just keeps trusting.

This guide walks you through a complete browser extension permissions audit — what every permission actually means, how to spot the dangerous ones, a step-by-step cleanup process for Chrome, Edge, Firefox, and Safari, and a practical schedule for keeping your browser clean going forward. By the end, you'll be able to look at any extension and decide in under a minute whether it deserves the access it's asking for.

Key Takeaways

• "Read and change all your data on all websites" is the single most dangerous permission — treat it as a red flag unless the extension's core function genuinely needs it.
• Extensions can be sold or hijacked after you install them, and your old permissions carry over to the new owner automatically.
• Audit your extensions every quarter, and immediately after any extension pushes an update that suddenly asks for new access.
• Use the browser's built-in "on click" or "on specific sites" site-access setting to limit even trusted extensions.
• Fewer extensions equals less attack surface. Uninstall anything you haven't used in 60 days.
• Cross-check unfamiliar developers the same way you'd verify open source software before installing it.

Why Browser Extension Permissions Are a Bigger Risk Than You Think

An extension runs inside your browser with a frightening amount of potential reach. Depending on what you've granted, it can read every page you load, capture what you type, see your cookies and session tokens, redirect your traffic, and quietly modify the content you see. That's not theoretical. It's the documented behavior of dozens of extensions that have been pulled from stores over the years.

The core problem is the permission lifecycle. You grant access once, during installation, when you're eager to use the thing. The browser then trusts the extension indefinitely. Three things can go wrong after that:

• The developer sells the extension. Buyers sometimes monetize the existing user base through ad injection, data harvesting, or worse. Your trust transfers with the sale.
• The developer's account gets phished. Attackers push a malicious update that inherits all your existing permissions, no new prompt required.
• The extension is abandoned. No updates means unpatched vulnerabilities, and a stale extension with broad permissions is a sitting target.

The defense is the same in all three cases: keep permissions minimal, and review them on a schedule. Just as you'd audit WordPress plugins for vulnerabilities before installing them, you need a deliberate process for the code running in your browser.

What Each Browser Extension Permission Actually Means

Permission warnings are written to be technically accurate and practically useless to a normal human. Here's what the most common ones translate to in plain language.

The high-risk permissions

• "Read and change all your data on all websites" ("<all_urls>" / host_permissions): The extension can see and alter every page you visit, including your bank, email, and internal company tools. This is the nuclear option.
• "Access your tabs and browsing activity" (tabs): The extension can see the URLs and titles of every tab you have open, even ones it doesn't directly interact with.
• "Read and change data on sites you visit" with broad patterns: Functionally similar to all-urls but scoped to common patterns like https://*/*.
• "Capture content of your screen" (desktopCapture): Self-explanatory and rarely necessary outside screen-recording tools.
• "Manage your downloads" (downloads): Can initiate or modify file downloads, a vector for dropping payloads.

The lower-risk permissions

• "Read and change data on [one specific site]": Scoped to a single domain. A Gmail extension that only touches mail.google.com is far safer than one touching everything.
• Storage (storage): Lets the extension save its own settings. Nearly harmless.
• Context menus, notifications, clipboard write: Convenience features with limited blast radius.

The rule of thumb: does the permission match the job? A dark-mode toggle that wants to read all your data on all websites is suspicious. A password manager that wants the same thing is expected, because it needs to detect login forms everywhere. Context decides.

How to Audit Extension Permissions Step by Step

Here's the full walkthrough. I'll cover Chrome and Edge together (they share the same engine), then Firefox and Safari. Budget about 20 minutes the first time.

Chrome and Microsoft Edge

1. Type chrome://extensions (or edge://extensions) into your address bar and press Enter.
2. Toggle Developer mode on, in the top right. This reveals each extension's ID and lets you inspect more detail.
3. For each extension, click Details.
4. Scroll to Site access. You'll see one of three settings: On click, On specific sites, or On all sites. Change anything set to "On all sites" to "On click" wherever the extension still works that way.
5. Note the Permissions list and ask whether each one fits the extension's stated purpose.
6. Check "View in Chrome Web Store". Look at the last-updated date, the developer name, and recent reviews mentioning ads or odd behavior.
7. If anything feels off, click Remove. You can always reinstall a legitimate tool.

Firefox

1. Open about:addons and select Extensions.
2. Click an extension, then open the Permissions tab.
3. Firefox lets you toggle optional permissions on and off individually. Disable anything non-essential.
4. Use the three-dot menu to Report or Remove as needed.

Safari

1. Open Safari > Settings > Extensions.
2. Select each extension and review what it can access — Safari shows per-site and "all websites" toggles clearly.
3. Set extensions to "Ask" for each website instead of granting blanket access.

A Worked Example: Auditing a Real 18-Extension Setup

Let me make this concrete with my own browser from a recent cleanup. I had 18 extensions installed. Here's what the audit found and what I did.

• 6 extensions had "on all sites" access. Three genuinely needed it (a password manager, an ad blocker, a grammar checker). The other three — a coupon finder, an old screenshot tool, and a "deals" extension I didn't remember installing — did not.
• 4 extensions hadn't been updated in over 14 months. Two of those were the coupon finder and the deals tool.
• 2 extensions had near-identical functionality (two different "tab manager" tools). I kept one.
• 1 extension requested the downloads permission but was just a font preview tool. Instant removal.

The result: I went from 18 extensions to 9. Of those 9, I switched 4 from "on all sites" to "on click." My browser's startup time dropped noticeably, and more importantly, I cut the number of extensions that could read my banking session from six to one (the password manager, which I trust and have protected with two-factor authentication).

The whole process took 22 minutes. The coupon extension, when I checked its store listing, had changed ownership eight months earlier and had a wave of recent one-star reviews complaining about injected ads. I'd dodged the exact problem my colleague hit.

Manual Audit vs Automated Tools vs Browser Settings: Which Approach Wins?

You have three broad ways to keep extensions in check. Each has tradeoffs, and the best setup usually combines them.

Approach	Effort	Catches hijacks?	Ongoing protection	Best for
Manual quarterly audit	Medium (20 min)	Yes, if you check update dates	Only when you do it	Everyone, as a baseline
Browser site-access limits ("on click")	Low (one-time)	Reduces blast radius	Continuous	Limiting trusted-but-broad extensions
Dedicated security extension/scanner	Low	Partially	Continuous	Less technical users
Separate browser profile for risky tools	Medium (setup)	Isolates damage	Continuous	Power users handling sensitive accounts

My recommendation: do a manual audit quarterly, lock everything to "on click" by default, and use a separate browser profile for anything experimental. Don't lean entirely on a security extension — remember, you'd be granting another extension broad permissions to police the others.

How to Limit Permissions Without Breaking

Cover image: computer by ph0rk, licensed under BY-SA 2.0 via Openverse.