The Firefox web browser displays extra permissions that an extension requests during installation and won't proceed with the installation until you activate the add button.

Extra permissions may request access to specific domains or all sites on the Internet, to display notifications, or to access the browser tabs.

You may notice sometimes that Firefox lists only some of the domains an extension requests access. Firefox displays a number, e.g. 13 other domains, in that case.

The prompt offers no option to display the entire list of domains an extension requests access to. You see such a prompt on the screenshot below.

Screenshot

The page of the extension on the Mozilla website lists the very same permissions so that it is not possible to verify all domains an extension requests access to using it or the installation prompt.

While it is certainly better if extensions requests access to as few domains as possible to provide its functionality, it is a usability issue that you cannot look the information up prior to the installation.

Here is a quick guide on how to display all domains without installing the extension.

Img

First the manual way:

1. Go to the page of the extension on the Mozilla website or third-party website.
2. Right-click on "add to Firefox" button and select the "Save link as" option.
3. Save the extension file to the local system.
4. Open the folder on the local device the extension was saved to.
5. If you have Bandizip or comparable software installed, right click on the file and select one of the available extraction options.
6. If you don't use a dedicated software for that, rename the file extension from xpi to zip.
7. Extract the Zip archive using Explorer.
8. Open the folder of the extracted archive.
9. Open manifest.json in a plain text editor, e.g. Notepad.
10. Check permissions; it lists all domains the extension requests access to and all other permissions the extension requests during installation.

Extension Source Viewer

Now with the help of the Firefox add-on Extension Source Viewer. We reviewed the extension back in 2016, check out the review for additional details. Chrome users can install this extension to verify Chrome extensions. You may also want to check out our precautions to take before installing Chrome extensions guide.

1. Install Extension Source Viewer in Firefox.
2. Right-click on the extension page and select "View extension source".
3. Select the manifest.json file to inspect it.
4. Check the listed domain permissions.

Tip: You may use a web version of Extension Source Viewer if you prefer not to install an extension to check other extensions.

Closing Words

Mozilla should consider adding an option to the extension page on the Firefox website and the installation prompt to list all domains an extension requests access to.

Anyone can simply add a domain that looks innocent and use that for whatever means.

Even legit services use whacky domain names, and I cant see even many techies from discerning legit from bad.

Just my two cents.