web_accessible_resources

As vezes, você precisa empacotar recursos — por exemplo, imagens, HTML, CSS ou Javascript — com a sua extensão e fazê-la acessível para as páginas web.

Por exemplo, a extensão de exemplo Beastify substitui uma página por uma imagem de um animal selecionado pelo usuário. As imagens foram empacotadas com a extensão. Para fazer visível a imagem selecionada, a extensão adiciona elementos <img> cujo atributo src aponta para a imagem do animal. Para que a página da web possa carregar as imagens, elas devem estar disponíveis na extensão.

With the web_accessible_resources key, you list all the packaged resources that you want to make available to web pages. You specify them as paths relative to the manifest.json file.

Note that content scripts don't need to be listed as web accessible resources.

If an extension wants to use webRequest (en-US) to redirect a public URL (e.g., HTTPS) to a page that's packaged in the extension, then the extension must list the page in the web_accessible_resources key.

For example, suppose your extension includes an image file at images/my-image.png, like this:

my-extension-files/
    manifest.json
    my-background-script.js
    images/
        my-image.png

To enable a web page to use an <img> element whose src attribute points to this image, you would specify web_accessible_resources like this:

"web_accessible_resources": ["images/my-image.png"]

The file is then available using a URL like:

moz-extension://<extension-UUID>/images/my-image.png"

<extension-UUID> is not your extension's ID. This ID is randomly generated for every browser instance. This prevents websites from fingerprinting a browser by examining the extensions it has installed.

The recommended approach to obtaining the URL of the resource is to use runtime.getURL passing the path relative to manifest.json, for example:

browser.runtime.getURL("images/my-image.png");
// something like:
// moz-extension://944cfddf-7a95-3c47-bd9a-663b3ce8d699/images/my-image.png

This approach gives you have the correct URL regardless of the browser your extension is running on.

web_accessible_resources entries can contain wildcards. For example, the following entry would also work to include the resource at "images/my-image.png":

  "web_accessible_resources": ["images/*.png"]

Note that if you make a page web-accessible, any website may link or redirect to that page. The page should then treat any input (POST data, for examples) as if it came from an untrusted source, just as a normal web page should.

"web_accessible_resources": ["images/my-image.png"]

Make the file at "images/my-image.png" web accessible.