permissions key to request special powers for your extension. This key is an array of strings, and each string is a request for a permission.
If you request permissions using this key, then the browser may inform the user at install time that the extension is requesting certain privileges, and ask them to confirm that they are happy to grant these privileges. The browser may also allow the user to inspect an extension's privileges after installation. As the request to grant privileges may impact on users' willingness to install your extension, requesting privileges is worth careful consideration. For example, you want to avoid requesting unnecessary permissions and may want to provide information about why you are requesting permissions in your extension's store description. More information on the issues you should consider is provided in the article Request the right permissions.
For information on how to test and preview permission requests, see Test permission requests on the Extension Workshop site.
The key can contain three kinds of permissions:
- host permissions
- API permissions
Host permissions are specified as match patterns, and each pattern identifies a group of URLs for which the extension is requesting extra privileges. For example, a host permission could be
The extra privileges include:
- XMLHttpRequest and fetch access to those origins without cross-origin restrictions (even for requests made from content scripts)
- the ability to read tab-specific metadata without the "tabs" permission, such as the
- the ability to inject scripts programmatically (using
tabs.executeScript()) into pages served from those origins
- the ability to receive events from the
webrequestAPI for these hosts
- the ability to access cookies for that host using the
cookiesAPI, as long as the
"cookies"API permission is also included.
- bypassing tracking protection for extension pages where a host is specified as a full domain or with wildcards. Content scripts, however, can only bypass tracking protection for hosts specified with a full domain.
In Firefox, from version 56 onwards, extensions automatically get host permissions for their own origin, which is of the form:
60a20a9b-1ad4-af49-9b6c-c64c98c37920 is the extension's internal ID. The extension can get this URL programmatically by calling
browser.extension.getURL(""); // moz-extension://60a20a9b-1ad4-af49-9b6c-c64c98c37920/
API permissions are specified as keywords, and each keyword names a WebExtension API that the extension would like to use.
The following keywords are currently available:
In most cases the permission just grants access to the API, with the following exceptions:
tabsgives you access to
privileged parts of thewithout the need for host permissions:
webRequestBlockingenables you to use the
"blocking"argument, so you can
modify and cancel requests.
downloads.openlets you use the
tabHidelets you use the
This permission is specified as
"activeTab". If an extension has the
activeTab permission, then when the user interacts with the extension, the extension is granted extra privileges for the active tab only.
"User interaction" includes:
- the user clicks the extension's browser action or page action
- the user selects its context menu item
- the user activates a keyboard shortcut defined by the extension
The extra privileges are:
- Access to the privileged parts of the tabs API for the current tab:
The intention of this permission is to enable extensions to fulfill a common use case, without having to give them very powerful permissions. Many extensions want to "do something to the current page when the user asks".
For example, consider an extension that wants to run a script in the current page when the user clicks a browser action. If the
activeTab permission did not exist, the extension would need to ask for the host permission
<all_urls>. But this gives the extension more power than it needs: it could now execute scripts in any tab, any time it likes, instead of just the active tab and only in response to a user action.
Note: You can only get access to the tab/data that was there, when the user interaction occurred (e.g. the click). When the active tab navigates away (e.g., due to finishing loading or some other event), the permission does not grant you access to the tab anymore.
Usually the tab that's granted
activeTab is just the currently active tab, except in one case. The
menus API enables an extension to create a menu item which is shown if the user context-clicks on a tab (that is, on the element in the tabstrip that enables the user to switch from one tab to another).
If the user clicks such an item, then the
activeTab permission is granted for the tab the user clicked, even if it's not the currently active tab (as of Firefox 63, bug 1446956).
There are two permissions which enables the extension to interact with the clipboard:
- Write to the clipboard using
- Read from the clipboard using
See Interact with the clipboard for more details.
Request privileged access to pages under
Request access to the privileged pieces of the
"permissions": ["*://developer.mozilla.org/*", "tabs"]
Request both of the above permissions.
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