The "activeTab" permission

The "activeTab" permission gives an extension temporary access to the currently active tab when the user invokes the extension - for example by clicking its action. Access to the tab lasts while the user is on that page, and is revoked when the user navigates away or closes the tab. For example, if the user invokes the extension on https://example.com and then navigates to https://example.com/foo, the extension will continue to have access to the page. If the user navigates to https://chromium.org, access is revoked.

This serves as an alternative for many uses of "<all_urls>", but displays no warning message during installation:

Without "activeTab":

Without activeTab

With "activeTab":

With activeTab

Example

See the Page Redder sample extension:

manifest.json:

{
  "name": "Page Redder",
  "version": "2.0",
  "permissions": [
    "activeTab",
    "scripting"
  ],
  "background": {
    "service_worker": "service-worker.js"
  },
  "action": {
    "default_title": "Make this page red"
  },
  "manifest_version": 3
}

service-worker:

function reddenPage() {
  document.body.style.backgroundColor = 'red';
}

chrome.action.onClicked.addListener((tab) => {
  if (!tab.url.includes('chrome://')) {
    chrome.scripting.executeScript({
      target: { tabId: tab.id },
      func: reddenPage
    });
  }
});

Motivation

Consider a web clipping extension that has an action and a context menu item. This extension may only really need to access tabs when its action is clicked, or when its context menu item is executed.

Without "activeTab", this extension would need to request full, persistent access to every website, just so that it could do its work if it happened to be called upon by the user. This is a lot of power to entrust to such a simple extension. And if the extension is ever compromised, the attacker gets access to everything the extension had.

In contrast, an extension with the "activeTab" permission only obtains access to a tab in response to an explicit user gesture. If the extension is compromised the attacker would need to wait for the user to invoke the extension before obtaining access. And that access only lasts until the tab is navigated or is closed.

What "activeTab" allows

While the "activeTab" permission is enabled for a tab, an extension can:

Invoking activeTab

The following user gestures enable the "activeTab" permission: