Browser extensions are invisible, always on, and operate with permissions most users granted without reading them. They sit between you and every website you visit, with the technical capability to see everything you type, every page you load, and in some cases every file you open in a browser tab.
A January 2026 report by Incogni analyzed 442 AI-powered Chrome extensions and found that 52% of them collect some form of user data, with a significant portion collecting personally identifiable information — personal communications, location, and detailed records of website content. That’s not a small category of obscure apps. It includes tools tens of millions of people use every day.
What Browser Extension Permissions Actually Mean
When you install a Chrome, Firefox, or Edge extension, it requests permission to do specific things. The permission language is technically accurate but deliberately vague in ways that obscure the real scope.
“Read and change all your data on websites you visit” — This is the broadest permission, and it’s common. It means the extension can read the text of every page you load, including pages where you’ve typed content. That includes your Gmail inbox, your bank’s transaction list, your company’s internal dashboard, any online text editor, and yes, every character you type into a form field before you hit submit.
“Read your browsing history” — The extension sees every URL you visit, including the timing of visits. Browsing history can be surprisingly revealing: medical information sites, legal research, financial services, relationship apps.
“Manage your downloads” — Access to what files you’ve downloaded and where they’re stored locally.
Not every extension requests all of these. But writing tools — the category most likely to be installed for productivity — commonly request broad read-write access across all sites, because that’s the only way they can function on any page you use.
The Grammarly and QuillBot Question
Grammarly and QuillBot are among the most installed browser extensions in the world. They also rank among the extensions flagged in privacy research for the breadth of data they can access.
To work, a writing assistant needs to read what you’re typing. That’s non-negotiable by function — an extension that can’t see your text can’t suggest corrections for it. The privacy question is what happens to that text beyond the moment of suggestion.
Grammarly’s privacy policy states that it uses content you write to improve its AI and to personalize features for you. QuillBot’s terms similarly describe using interaction data for product improvement. Both companies present this as standard product improvement — and it is fairly standard for AI products. What makes it different from, say, a stand-alone writing app is the scope: these extensions see your text across every site you use, not just within a single application.
For most writing — professional emails, public-facing content, social media posts — the privacy implications are minor. For content that’s sensitive by nature — private messages, legal documents, medical notes, personal journal entries typed anywhere online — the relevant question is whether you intended that content to enter an AI improvement pipeline when you wrote it.
Supply Chain Attacks: When Trusted Extensions Turn Malicious
The greater risk for many users isn’t the extensions they know are collecting data. It’s the ones that were safe when they installed them and aren’t anymore.
Security researchers have documented a pattern in which extensions with clean track records are purchased by new owners or compromised by malicious actors, then quietly updated to harvest data they weren’t collecting before. These attacks are effective specifically because they exploit existing trust — an extension you installed two years ago and stopped thinking about is more dangerous than one you’d scrutinize today.
In well-documented cases, extensions operated benignly for five years or more before being weaponized. The transition from clean tool to data exfiltration happens through a routine extension update — the same mechanism that keeps extensions functioning correctly — with no notification to the user.
In early 2026, security researchers uncovered over 30 fake AI-themed Chrome extensions that had collectively accumulated more than 300,000 installs before being identified. These extensions mimicked the names and icons of legitimate productivity tools while collecting browsing data and sending it to external servers.
Browser vendors have improved their review processes since these incidents. The removal lag between a compromised extension being identified and being removed from the store remains a meaningful window of exposure.
What Extensions See That You Might Not Expect
The access problem isn’t just about text you’re actively writing. It’s about everything loaded in your browser.
Email. If you use Gmail, Outlook, or any webmail in Chrome with extensions installed that have broad site permissions, those extensions can read your inbox — messages you receive, not just messages you compose.
Internal tools. Corporate dashboards, project management tools, internal wikis, CRM systems — anything accessed via browser is readable by extensions with appropriate permissions. A Grammarly install on a work laptop can technically see the contents of your company’s Salesforce instance.
Financial information. Banking sites, brokerage accounts, crypto exchanges accessed in browser are within scope.
Personal notes in web apps. Notion, Google Docs, online journals, web-based diary tools — anything you type in a browser tab is readable by extensions with the right permissions.
The extensions you think of as grammar checkers are, architecturally, privileged readers of nearly everything you do in your browser.
How to Audit Your Extensions Right Now
The process takes about five minutes and is worth doing if you haven’t looked at your installed extensions recently.
In Chrome: Click the puzzle-piece icon in the toolbar or navigate to chrome://extensions. Review each installed extension — ones you don’t recognize or no longer use should be removed immediately.
Check permissions. Click “Details” on each extension you keep, then “View permissions” to see exactly what it can access. Extensions with “Read and change all your data on websites you visit” have the broadest access.
Look for extensions you didn’t install intentionally. Software bundles, browser updates, and app installations sometimes add extensions silently. If you see anything unfamiliar, remove it.
Disable, don’t just turn off. Extensions set to “off” in Chrome still load in your browser profile; removing them is the only way to fully eliminate access.
For extensions you actively use and want to keep, consider whether you need them enabled on all sites or only on specific domains. Chrome allows you to limit extension access to specific sites via the extension’s permissions settings — a grammar checker doesn’t need access to your bank’s site.
The Risk of Writing Private Content in Browser-Accessible Apps
The most practical implication of extension permissions isn’t about Grammarly specifically. It’s about where you put content you consider private.
Any text typed into a browser tab is readable by extensions with appropriate permissions. Web-based notes apps — Notion, Roam, Obsidian Publish, online journals, browser-tab diary tools — are all within scope. If you write about personal medical history, relationship events, financial details, or anything you’d classify as genuinely private inside a browser tab while writing extensions are installed, that content is technically accessible.
This isn’t an argument against online notes apps generally. It’s a prompt to notice the difference between “stored privately” and “typed in my browser tab with writing tools installed.”
The cleanest architecture for genuinely private writing is a dedicated mobile or desktop app that doesn’t run in the browser at all — one whose text input isn’t visible to any Chrome extension, regardless of what that extension is permitted to read.
What to Remove Today
A few specific categories worth prioritizing in any extension audit:
Extensions from developers you don’t recognize. The Chrome Web Store lists the publisher of every extension. If the company name means nothing to you and the extension has broad permissions, the combination warrants removal.
Old coupon and deal-finding extensions. These frequently request browsing history and site data access. Their business model often depends on the data they collect, not just the affiliate commissions they earn from purchases.
Extensions you installed for a one-time task. If you added something to do a specific job months ago and haven’t thought about it since, it’s been silently running in your browser ever since.
Redundant tools. If you have three ad blockers or two grammar checkers, the extra ones are only adding attack surface.
The goal isn’t to run a browser with no extensions — many are genuinely useful and behave responsibly. It’s to run a browser where every installed extension was installed intentionally, has a clear purpose you still need, and has permissions proportionate to that purpose.