chrome:// urls are blocked for security reasons. Google doesn’t want you to change the appearace or change chrome settings without the user knowing it. when you load your extension, it immediately executes those files inside the chrome://extensions page. If you want to execute your script in every tab the user goes to, you should use:
chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
//code in here will run every time a user goes onto a new tab, so you can insert your scripts into every new tab
});