When you install a browser extension, a pop-up lists what it "can access". Most people click through without reading it. That list is the single clearest signal of whether an extension is trustworthy — and it is the one thing most people ignore.
This guide explains what each common permission actually lets an extension do, what it does not do, and how to decide whether to grant it.
The permission that matters most: "Read and change all your data on all websites"
This is the broadest permission an extension can request. It allows the extension to:
- See every page you visit and everything on it, including form fields, passwords, and payment details.
- Modify the content of any page (inject ads, change links, rewrite text).
- Send data from any page to a remote server.
Legitimate uses: ad blockers, password managers, and developer tools all need this permission to work. The question is not whether the extension asks for it — it is whether the extension deserves it.
What to ask: Does this extension's purpose require access to every site? A password manager does; a simple calculator extension does not. If the permission seems too broad for the extension's job, that is a red flag.
"Storage" — less dangerous, still worth understanding
This permission lets the extension save data to your browser's local storage. It is used for legitimate purposes — saving settings, storing cached data, and keeping session information. It is a low-risk permission on its own, but it becomes dangerous when combined with "read all data" because the extension can then read and exfiltrate everything it stored.
"Tabs" — what the extension can see about your open tabs
This permission lets the extension see the URLs of your open tabs, the title of each tab, and the tab's status. It does not let the extension read the content of the page inside the tab — that requires "read all data" or "activeTab". Legitimate uses: tab management extensions, session managers, and search tools that index your open tabs.
"ActiveTab" — a safer alternative to "read all data"
This permission gives the extension access to the current tab, but only when you interact with the extension (clicking its toolbar icon or using a keyboard shortcut). It is a more restrictive permission that many well-designed extensions use instead of asking for all-site access. If an extension can do its job with activeTab, it should ask for activeTab — not for "read all data".
"Cookies" — access to your cookies
This permission lets the extension read, create, and modify cookies for any site. It is a powerful permission because cookies contain login tokens, session identifiers, and tracking data. Legitimate uses: cookie managers, session managers, and developer tools. If an extension asks for this permission, ask why — a simple ad blocker does not need it.
"WebRequest" — intercepting network requests
This permission lets the extension intercept, block, or modify network requests made by the browser. It is used by ad blockers (to block tracking scripts), developer tools, and security extensions. Legitimate uses are common, but the permission is powerful: an extension with webRequest can see every request your browser makes and decide what to do with it.
"Notifications" — sending alerts to your desktop
This permission lets the extension show notifications on your desktop. It is low-risk on its own, but it is a vector for spam and scams if the extension is malicious. If you notice unexpected notifications after installing an extension, check this permission.
How to review permissions after installation
You can check what an extension can access at any time:
- Chrome:
chrome://extensions/→ click "Details" on the extension → scroll to "Permissions". - Firefox:
about:addons→ click the extension → "Permissions". - Edge:
edge://extensions/→ click "Details" → "Permissions".
If you see a permission that seems too broad, you can often adjust it. Chrome lets you limit some extensions to specific sites, and Firefox lets you grant permissions on a per-request basis for some extensions. Our how to check extension permissions guide shows the exact steps for each browser.
The permission that should never be granted
- "Native messaging" — allows the extension to communicate with a program installed on your computer. This is a bridge between the browser and your system, and it can be used to run commands on your computer. Only grant this to extensions you deeply trust, and only when the extension's purpose requires it (a companion app for a password manager, for example).
The honest rule
The safest approach is not to become an expert in every permission. It is to keep your extension list short. The fewer extensions you install, the fewer permission pop-ups you need to evaluate. When you do install one, read the permission list — and if it asks for more than you expect, find an alternative. Our how to choose safe browser extensions guide covers the full vetting process.
Quick answers
What does "read and change all your data on all websites" mean? The extension can see every page you visit and everything on it, including form fields, passwords, and payment details. It can also modify pages and send data to remote servers.
Is it safe to grant this permission to a password manager? Yes — a password manager needs it to fill in credentials on any site. The question is whether the extension is trustworthy, not whether the permission is justified.
Can I limit an extension to specific sites? Chrome lets you restrict some extensions to specific sites. Firefox does not have a built-in equivalent, but you can use the "activeTab" permission model for extensions that support it.
What should I do if an extension asks for more permissions than expected? Do not install it. Look for an alternative that asks for fewer permissions, or check the developer's reputation before granting broader access.
Sources and further reading
- Chrome: Extension permissions
- Mozilla: Permission requests
- How to check extension permissions
- How to choose safe browser extensions
Written by Hassan Arshad, founder of UsefulOrbit. Last updated August 31, 2026.