Over 40 Malicious Firefox Extensions Target Crypto Wallets: How to Protect Your Digital Assets Now

If you’re passionate about cryptocurrency, you know that security is everything. But what if I told you that the biggest threat to your crypto isn’t a phishing email or a suspicious website—but a browser extension you trusted? Recent research has uncovered a massive, ongoing campaign where over 40 malicious Mozilla Firefox extensions have been targeting cryptocurrency wallets, silently stealing users’ digital assets. Sound alarming? It should be, but don’t worry—I’m here to break down what’s happening, how it impacts you, and what you can do to stay safe.

The Growing Threat: Malicious Firefox Extensions & Crypto Theft

Let’s start with the basics. Browser extensions have become an everyday part of our online lives. They add convenience, help us manage tasks, and—especially in the world of crypto—often serve as the bridge between you and your digital wallet. But this convenience can come at a steep cost.

What Exactly Happened?

Cybersecurity researchers at Koi Security recently discovered more than 40 rogue Firefox add-ons masquerading as legitimate crypto wallet tools. These extensions copied the names, branding, and even the open-source code of popular wallets like Coinbase, MetaMask, Trust Wallet, Phantom, Exodus, OKX, Keplr, MyMonero, Bitget, Leap, Ethereum Wallet, and Filfox.

Here’s why that matters: If you’re like most crypto users, you rely on browser extensions as a quick gateway to your funds. But these malicious clones don’t just look like the real deal—they behave like it, too. The difference? Hidden within their code are data-stealing functions designed to snatch your wallet keys and seed phrases, sending them quietly to an attacker’s remote server.

How These Malicious Extensions Work (And Why They’re So Dangerous)

Unlike traditional phishing scams that trick you into entering your credentials on a fake website, these browser extensions are much sneakier. Once installed, they operate inside your browser, giving attackers direct access to everything you type or click related to your wallet.

Let me explain with an analogy: Think of a malicious extension as a lockpick cleverly disguised as your house key. You trust it to open the door to your digital safe, but it makes a copy of your valuables each time you walk in. Not only does it snatch your wallet secrets, but in some cases, it also collects your external IP address—making it easier for attackers to track or target you further.

Why Are They So Hard to Spot?

Malicious extensions have become more sophisticated than ever:

Impeccable Imitation: They use the same names, logos, and UI as trusted wallet tools.
Open-Source Copycats: By cloning legitimate, open-source code, they maintain the expected look and feel, making detection even tougher.
Fake Reviews Galore: Hundreds of glowing 5-star reviews (well beyond the actual user base) create a façade of trust.
Official Add-On Store Presence: These extensions weren’t just floating around in obscure corners of the web—they were uploaded directly to the Firefox Add-ons store, making them seem legitimate.

Key Takeaway: Traditional security tools often can’t detect these extensions because they blend in so well with the real thing. That’s why it’s crucial to approach all browser extensions, especially crypto-related ones, with skepticism.

Real-World Impact: What Could Happen If You’re Infected?

So, what happens if you unknowingly install one of these malicious add-ons? Here’s the frightening reality:

Stolen Wallet Keys & Seed Phrases
The moment you interact with your wallet, the extension can silently intercept your sensitive data.
Immediate Loss of Funds
Attackers use stolen credentials to transfer your assets out—sometimes within minutes. For many, there’s no recourse.
Potential Targeting of Other Accounts
Your IP address and browsing behavior may be tracked, opening you up to further targeted attacks.
Loss of Trust in Platforms
Even major names like Coinbase and MetaMask aren’t immune to impersonation, which can undermine your trust in the broader crypto ecosystem.

This isn’t a theoretical risk—it’s happening right now. The campaign has been active since at least April 2025, with some extensions uploaded just last week and only recently removed.

The Anatomy of the Attack: Techniques & Tactics

Let’s take a closer look at how these attackers have managed to pull off such a large-scale campaign.

1. Impersonation Through Open-Source Cloning

Most popular wallet extensions are open-source, meaning anyone can access their code. Attackers take this code, inject their own malicious scripts, and re-upload it under the same or very similar branding. It’s the digital equivalent of making a copy of a famous painting and swapping it into a gallery.

2. Artificially Inflated Popularity

Hundreds of fake, glowing reviews make these extensions look like must-have tools. But simple math reveals something suspicious: The number of 5-star reviews often far exceeds the number of actual active users. This manipulation is designed to lure people into a false sense of security.

3. Trusted Storefronts

Uploading these malicious add-ons to the official Firefox store adds an extra layer of deception. If it’s on the store, it must be safe, right? Unfortunately, not always—which brings us to the limitations of official vetting processes.

4. Stealth & Persistence

By operating from within your browser, these extensions avoid many traditional endpoint security solutions. They don’t need you to click on a sketchy link or download a suspicious file. They simply wait for you to interact with your wallet, then quietly siphon off your secrets.

Who’s Behind the Attack? Clues Point to a Russian-speaking Group

While attribution in cybercrime is always tricky, researchers have found Russian language comments in the source code and metadata from PDF files linked to the attackers’ command-and-control servers. This suggests a Russian-speaking threat actor group is behind the campaign.

Why does this matter? Knowing who’s behind an attack can help security teams anticipate future tactics and improve detection. But for everyday users, the crucial lesson is clear: The threat is sophisticated and highly motivated.

Mozilla’s Response: An Early Detection System

Mozilla has moved quickly to mitigate the risk. All identified malicious add-ons (except one, “MyMonero Wallet”) have been removed from the Firefox Add-ons store. More importantly, Mozilla has announced an “early detection system” to spot scam crypto wallet extensions before they gain popularity.

But as history shows, attackers are creative and persistent. No system is foolproof. That’s why personal vigilance remains your best defense.

Practical Steps: How to Protect Your Crypto Assets from Malicious Extensions

Now for the most important part—what can you do to keep your digital assets safe?

1. Vet Every Extension—Even in Official Stores

Don’t assume that just because an extension is available on the Firefox Add-ons store, it’s safe. Before installing:

Check the Developer: Look for extensions published by verified, recognizable organizations.
Read Recent Reviews Critically: If there are hundreds of 5-star reviews but few detailed comments, be wary.
Check the Number of Users: A brand-new extension with hundreds of reviews is a red flag.
Visit Official Project Sites: Download wallet extensions only from the official site of the wallet provider, or by following their direct links to browser store listings.

2. Limit Installed Extensions

Only keep essential extensions. Every add-on increases your attack surface. Regularly review and prune extensions you no longer use or don’t fully trust.

3. Monitor Permissions Closely

Don’t grant unnecessary permissions. If an extension asks for access beyond what’s needed for its basic function, that’s a warning sign.

4. Regularly Audit Your Wallet Activity

Check your wallet transaction history for any unauthorized activity, and enable alerts where possible.

5. Use Security Tools & Multi-Factor Authentication

Consider wallet providers that add extra layers of security, such as hardware wallets or multi-factor authentication (MFA). This won’t prevent extension-based theft if your seed phrase is intercepted, but it can slow attackers and buy precious time.

6. Stay Informed on Latest Threats

Follow reputable cybersecurity news sources, such as Krebs on Security or The Record by Recorded Future, to keep up with the latest threats affecting crypto users.

What to Do If You Think You’ve Installed a Malicious Extension

Let’s be real—mistakes happen. If you realize you may have installed a rogue wallet extension:

Immediately Remove the Extension
Delete the suspicious add-on from your browser.
Change Your Wallet Credentials
If your seed phrase or keys were exposed, consider your wallet compromised. Move your assets to a new wallet with a fresh seed phrase.
Check for Unauthorized Transactions
Review your wallet history and alert your provider if you spot anything unusual.
Scan Your System
While browser extensions are the main risk, it never hurts to run a reputable malware scan on your machine.
Report the Extension
Notify Mozilla and the original wallet provider to help prevent further victims.

Why This Matters: The Bigger Picture for Crypto Security

This campaign is a wake-up call for everyone in the crypto space. As digital assets become more mainstream, attackers are adapting—using clever, low-effort, high-impact methods to target everyday users.

It’s a reminder that the tools we trust most can sometimes become our greatest vulnerabilities. But with awareness and proactive security habits, you can dramatically reduce your risk.

Frequently Asked Questions (FAQ)

Q: How can I tell if a Firefox extension is safe for my crypto wallet?
A: Always download from the official wallet provider’s website or verified publisher on the Firefox Add-ons store. Check for detailed, recent reviews and be suspicious of extensions with little history or an unusually high number of positive reviews. Limit permissions and keep your browser and extensions updated.

Q: What should I do if my crypto wallet is compromised by a malicious extension?
A: Immediately remove the extension, transfer funds to a new wallet with a fresh seed phrase, scan your computer for malware, and notify both Mozilla and your wallet provider.

Q: Are Chrome or other browser extensions also at risk?
A: Yes, while this campaign targeted Firefox, similar threats exist in other browsers. Always exercise caution, regardless of browser choice.

Q: Can official stores like the Firefox Add-ons store guarantee my safety?
A: No system is 100% secure. While official stores have vetting processes, attackers can sometimes slip through. Always verify before you install.

Q: Why do attackers target crypto wallets?
A: Cryptocurrency is valuable, largely non-reversible, and often anonymous—making it a perfect target for cybercriminals.

Q: How often should I review my extensions?
A: At least once a month, or immediately if you notice anything suspicious with your wallet or browser behavior.

Q: Where can I learn more about staying safe in crypto?
A: Check out resources from Coinbase’s security center, MetaMask safety tips, and leading cybersecurity blogs.

Final Thoughts: Stay Vigilant, Stay Secure

The discovery of over 40 malicious Firefox extensions preying on crypto users is a stark reminder: In the digital world, trust is earned, not given. By taking a few proactive steps—vetting extensions, limiting permissions, staying informed—you can dramatically reduce your risk.

If you found this guide helpful, consider subscribing or exploring our in-depth articles on cryptocurrency safety and browser security. Your digital assets are worth protecting—don’t leave it to chance.

Stay safe out there, and remember: In crypto, security isn’t just a feature. It’s a mindset.

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Over 40 Malicious Firefox Extensions Target Crypto Wallets: How to Protect Your Digital Assets Now