Inspect Firefox WebExtensions storage.local

Question

WebExtensions can store data locally in their storage.local . Apparently it is a key-value store and the values can be primitive types (such as numbers, booleans, and strings) or Array types.

I want to inspect what a particular WebExtension (not made by me) is storing in this area.

How can this be done?

Bonus for methods that can be automated, allowing me to extract the data from a bash script. But GUI solutions are very acceptable too.

Answer 1

In Firefox

• enter about:debugging into the navigation bar and hit enter
• check Enable add-on debugging at the very top of that page
• below that you can see a list of all installed extensions. Find the one you want to inspect and click its debug link.
• An Incoming Connection prompt will show. Click OK to allow it.
• In the new pop up switch to the Console tab
• Here you can execute code in the context of the extension

• Paste the following code to get the storage.local content:

   chrome.storage.local.get(null, function(items) { console.log(items); }); 

Edit:

If you want to download the object you could stringify it, create a blob from it and then create a data URL from the blob and open it in a new tab or download it. Like this:

chrome.storage.local.get(null, function(items) {
    var blob = new Blob([JSON.stringify(items, null,'  ')], {type: "text/plain"});
    var url = URL.createObjectURL(blob);
    chrome.tabs.create({ url: url }); // requires that the extension has the "tabs" permission
    //chrome.downloads.download({ url: url }); // requires that the extension has the "downloads" permission
});

The target extension needs to have the "tabs" permission to open a tab or the "downloads" permission to start a download. You could also look for other ways of accessing the data. For instance through a "browserAction"/"pageAction"-popup or by sending an ajax call to an external server submitting the data in the post body...

Answer 2

To access the data from Bash you could try to read it from the storage.js file of the extension. You should find it in your home directory (Linux). For me it was under: ~/.mozilla/firefox/{profile}/browser-extension-data/{extension}/storage.js . On Windows it would be somewhere in appdata. On OS XI don't know.

The storage.js file is a json file.

I wouldn't rely on that working in the future. Firefox might switch to storing the data in an encrypted format at some point. Also don't rely on the data being up to date. Firefox might not sync the storage with the file on disk immediately.