The average internet user has 5-10 browser extensions installed, yet rarely reviews their permissions or creators. That innocent-looking coupon finder or grammar checker might be the digital equivalent of leaving your front door unlocked. Today, I’m taking a break from discussing my upcoming book to focus on a cybersecurity risk that’s literally hiding in plain sight: browser extensions.

The Convenient Danger

Browser extensions enhance our online experience in countless ways—they block ads, manage passwords, check grammar, find deals, and organize our tabs. They’re productivity boosters and time-savers that most of us install without a second thought. But here’s the uncomfortable truth: these helpful tools can pose serious security and privacy risks.

Recently, researchers at McAfee identified over 1,500 malicious extensions across various browsers that collectively had more than 20 million downloads. These extensions weren’t just collecting basic data—many were harvesting passwords, tracking browsing history, injecting ads, and even participating in credential theft.

Why Extensions are Risky

What makes browser extensions particularly dangerous is their elevated access to our digital lives:

  1. Deep Browser Access: Unlike websites, which run in sandboxed environments, extensions often have permissions to read and change all your data on websites you visit. Think about what that means—they can see everything from your banking details to your private messages.
  2. Legitimate Turned Malicious: Many extensions start legitimate but turn malicious after an ownership change or update. A 2024 study from the University of California found that 4% of popular Chrome extensions changed ownership at least once, with nearly a third of those subsequently engaging in suspicious behavior.
  3. Limited Vetting: While browser stores have improved security measures, their vetting processes aren’t foolproof. Extensions with malicious code can slip through or introduce it after approval through updates.
  4. Data Harvesting: Even ‘legitimate’ extensions may collect and sell your browsing data. According to a report from the Electronic Frontier Foundation, nearly 40% of popular browser extensions collect more data than necessary for their stated functionality.

Do Browsers Verify Extensions They Offer for Download?

Yes, major browsers like Firefox, Edge, Chrome, and Brave all have mechanisms in place to check the safety of extensions before installation, though the specifics of their approaches differ:
  • Google Chrome: Chrome relies on the Chrome Web Store, where extensions are reviewed before being published. Google uses automated scans and manual reviews to detect malicious behavior, policy violations, or security risks. However, some risks can slip through, especially with updates to existing extensions. Chrome also warns users if an extension is from an unverified source outside the Web Store.
  • Mozilla Firefox: Firefox extensions are hosted on the Mozilla Add-ons site (AMO). Mozilla conducts a review process that includes automated checks and, in some cases, human review to ensure extensions comply with security and privacy policies. Since Firefox transitioned to the WebExtensions API (similar to Chrome), the review process has become stricter, but users can still sideload extensions, bypassing these checks with a warning.
  • Microsoft Edge: Edge uses the Microsoft Edge Add-ons store, where extensions undergo a vetting process for security, privacy, and functionality. Since Edge is Chromium-based, it can also install Chrome Web Store extensions, but it warns users about potential risks from third-party sources. Microsoft employs automated scans and occasional manual reviews.
  • Brave: Brave, also Chromium-based, primarily pulls extensions from the Chrome Web Store, inheriting Google’s review process. Brave doesn’t host its own extension marketplace but emphasizes privacy and security by default (e.g., blocking trackers). It warns users about unverified extensions and restricts some permissions unless explicitly allowed.

In all cases, the safety checks aren’t foolproof—malicious extensions can occasionally bypass initial reviews, especially if they hide bad behavior or introduce it in updates. Each browser also allows sideloading (installing extensions manually), which skips these checks and comes with a risk warning. For the best protection, sticking to verified extensions from official stores and checking user reviews or permissions is a smart move.

My Recent Close Call

While researching statistics for my cybersecurity book, I nearly fell victim myself. I discovered an extension I’d installed months ago—supposedly to optimize my browser’s memory usage—was actually tracking every site I visited and sending the data to an unknown server.

The irony wasn’t lost on me: here I was writing about protecting your digital identity while unwittingly compromising my own. It was a (yet-again) humbling reminder that vigilance is a practice, not a one-time action.

Protecting Yourself with an Extension Audit

Having spent months researching these techniques for my cybersecurity book, I can offer these practical safeguards:

  1. Review Current Extensions: Open your browser extension menu (usually found in the top-right corner) and list all installed extensions.
  2. Check Permissions: For each extension, review what permissions it requires. Be especially wary of those requesting access to “read and change all data on websites you visit” or “access browser tabs.”
  3. Research Creators: Who made the extension? Is it from a known company with a reputation to protect, or an obscure developer with no digital footprint?
  4. Consider Necessity: Do you actually use this extension regularly? If not, remove it. Security experts recommend keeping extensions to a minimum—only those providing substantial value worth the risk.
  5. Update or Remove: Make sure your useful extensions are updated, and ruthlessly remove any you don’t recognize, don’t need, or that request excessive permissions.

I performed this audit myself last week and was shocked to find I had 14 extensions installed across browsers—four of which I hadn’t used in months, and three with suspiciously broad permissions.

In Summary

Just as we’re encouraged to regularly change passwords or update software, consider adding a quarterly “extension audit” to your digital maintenance routine. It takes less than 15 minutes but significantly reduces your exposure to potential threats.

This simple practice exemplifies the core philosophy of my upcoming book: effective cybersecurity isn’t about technical complexity—it’s about maintaining mindful awareness of our digital environments.

What browser extensions do you currently have installed? Have you ever reviewed their permissions? Let me know in the comments below—I’d love to hear if this prompted you to conduct your own audit!

What’s Next

Adventures of a Sage is currently exploring personal cybersecurity topics to help everyday users protect their digital lives. Follow along as I share insights from my journey writing a comprehensive book about this topic.

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