How to Build a React Chrome Extension That Doesn’t Break the Web

10 Rules for Injecting React Without Breaking Gmail, YouTube, or Your Reputation

I’ve been writing React for over half a decade, but only recently decided to vibe-code my own browser extension — no plan, no spec, just vibes. Along the way, I learned a few things the hard way about how React and the open web don’t always get along. If you’re building a React-powered extension and want to avoid blowing up someone else’s website, here’s what I wish I knew before I hit “deploy.”

React is a fantastic framework for building rich, interactive UIs. It’s no wonder many developers reach for it when creating Chrome extensions. The problem? Most of the internet wasn’t built with your React app in mind.

Injecting a full-blown React UI into someone else’s meticulously optimized site can feel like tossing a raccoon into a ballet. You’ll crash layouts, break logins, trip CSPs (Content Security Policies), or worse — get delisted from the Chrome Web Store.

I’ve been there. So before you deploy, here are ten field-tested rules to help your React-powered extension be powerful and polite.

Be Surgical With Your URL Matches

In manifest.json, don’t blindly use:

"matches": ["<all_urls>"]

This is the nuclear option. If you must use it, pair it with exclude_matches to avoid fragile sites like:

"exclude_matches": [
  "https://www.google.com/*",
  "https://mail.google.com/*",
  "https://accounts.google.com/*",
  "https://twitter.com/*",
  "https://www.facebook.com/*"
]

These sites are notoriously reactive to DOM changes, and even a small injected React component can cause visual glitches, layout shifts, or security flags.

Namespace Your Styles

React’s scoped components are helpful, but your styles can still bleed into the page — especially when using global styles or component libraries.

Do this:

• Use CSS Modules
• Prefix everything (.rocket-button, .hie-card)
• Avoid styled-components with global styles unless you're wrapping them in a Shadow DOM (more on that next)

A good rule: Pretend your styles are entering a minefield.

Avoid Login, Checkout, and Admin Routes

Don’t inject your React app onto sensitive pages like /login, /checkout, /cart, or /admin.

You can filter at runtime:

if (window.location.pathname.match(/(login|checkout|admin)/)) return;

Or better yet, exclude those URLs entirely in your manifest. If your extension breaks an authentication or purchase flow, users will disable it fast — and Chrome reviewers might too.

Don’t Leave StrictMode On in Production

React.StrictMode is great for catching bugs in development—but it intentionally double-invokes some lifecycle methods, which can be jarring in production.

root.render(
  process.env.NODE_ENV === 'development' ? (
    <React.StrictMode><App /></React.StrictMode>
  ) : (
    <App />
  )
);

This tiny toggle avoids unexpected behavior once you’re live.

Optimize Your Bundle (Size Matters)

React is powerful — but heavy. Shipping a 500KB+ UI for a tooltip is overkill.

Some tips:

• Tree-shake with webpack or Vite
• Avoid full design systems like MUI unless you’re using < 10% of it
• Use lighter UI libs like shadcn/ui or Radix Primitives
• Analyze your final build with webpack-bundle-analyzer

Every kilobyte counts, especially if you’re injecting into every page load.

Clean Up After Yourself

If you inject UI on demand (e.g., when a user clicks a button), make sure you unmount your React app and remove DOM nodes:

ReactDOM.unmountComponentAtNode(container);
container.remove();

This is critical on SPAs where navigation doesn’t reload the page. Leaving DOM nodes around will cause memory leaks and duplicate interfaces.

Respect CSP (Content Security Policy)

Many popular websites have CSP headers that disallow:

• Inline scripts
• Inline styles
• eval or new Function

React + Webpack or Vite bundles are fine if you avoid:

• dangerouslySetInnerHTML
• Third-party scripts or style loaders
• Dynamic Function() usage

When in doubt, test your extension on sites with strict CSPs (like google.com) and look for red flags in DevTools → Console.

Final Thought: Be a Good Web Citizen

Building a React-based browser extension gives you superpowers. But the web isn’t your playground — it’s someone else’s carefully tuned environment.

The best extensions enhance the browsing experience while remaining invisible unless needed. They load fast, clean up after themselves, and never assume they own the DOM.

Build like you’re a guest. That’s how you get invited back.

Bonus: Want to See a Real React Extension Done Right?

Check out Hi Energy Rocket, a React-based Chrome extension that helps publishers track and discover affiliate programs as they browse. It’s lightweight, isolated, and built to stay out of your way — no DOM drama, no performance hit.

You can try it now on the Chrome Web Store.

Tried it? Let me know what breaks, what works, and what you’d improve.
Your critique helps me level up — and keep building extensions that don’t break the internet.