Develop Reference

Should chrome extensions have access to Tabs content (other websites)

Is there a way to identify and block JS files/events that are not part of your domain?
Like assume, if I'm writing a extension for chrome and I put following code in my JS
$('div').on('click', function(){ alert("yup"); });
is there a way for a website to handle this case?
Edit 1:
After discussion with #Clive, I realized that all extension/application should run in sandbox and should not be able to access events/elements outside the scope.
Case
A chrome extension have a keypress event on input[type=text] and input[type=password]. Now this extension runs in background, so there JS files are always available. Hence if you open facebook and login to your account, this extension will capture data and can send it to its server.
My Case
Two user was getting alert messages multiple times. Initially we thought its a part of our code and checked all JS files. But then realized, both user had same extension and so we diagnosed that extension's JS file and found alert in it. Now we were lucky, no damage was done, but it still posses a possible security threat.

Short answer: No.
Long answer:
Chrome extensions run their code in a separate space from your site's code, so they don't interact at all. The best you could do is prevent DOM edits. Luckily chrome extensions already run in a sandbox and have to explicitly ask for permissions for the domains that they inject code in and those domains are all listed when you install an extension. The only other way for extensions to interact with a page is through the activeTab permission which is a one time allowance on a specific user action. If you are using an extension that you think is malicious, you can always just read the code since JS is naturally open source. It really all boils down to a matter of trust. Installing something is explicitly trusting that thing to not mess up your stuff. This applies to all programs. If you don't trust an extension, then don't install it. A sandbox can only prevent so much while still letting extensions do something.

My chrome extension is pretty large and event driven. What are some ways I can optimize?

I have created a chrome extension which is quite big. It relies on external frameworks as well as custom code. The extension manipulates the DOM and my fear is that it would really slow chrome down for some users especially if it is loaded on every tab.
Questions
Are chrome extensions loaded per tab?
Is there an upper or suggested limit to how big your extension should be?

Extensions downloaded by the Chrome browser upon install are subsequently run off of the local disk in order to speed up performance. If a new version of the extension is pushed online, it will be automatically downloaded in the background to any users who have the extension installed.
Answer to the second one I don`t think so.

I can only answer the first question:
chrome extension code might be injected to web page using content script, you need to specify which host you want to inject script to.
So it is not a question of will chrome extension be loaded per tab, you need to specify whether you want your extension to load per tab.
You can request the extension to load only in the web sites that you want it to load.
see content script here

How to fix Google Analytics "analytics.js" net::ERR_FILE_NOT_FOUND?

The relevant line of the Google script is:
(window,document,'script','//www.google-analytics.com/analytics.js','ga');
I am running this particular file locally (as in, I double-click "index.html" on Windows Explorer and it opens in Chrome.
After about a minute of trying to load this file it fails with net::ERR_FILE_NOT_FOUND reported in the Developer Console.
I understand why this is happening, it is trying to load this as a local file. If I do this it works just fine:
(window,document,'script','www.google-analytics.com/analytics.js','ga');
In other words, I eliminated the //. This would work just as well:
(window,document,'script','http://www.google-analytics.com/analytics.js','ga');
Is going explicitly doing it this way to only track real websites?
If so, how are you dealing with this issue for local development?
I do run a VM with Ubuntu server for local development of more elaborate sites. In this case I was working on a single file landing page that I knocked out quickly and wanted to just test just as easily but ran into the browser hanging waiting for analytics.js
Is it safe to remove the // or add http: in general terms. I don't generally like to modify Google code unless I fully understand why they are doing things in a specific way and what the consequences of my actions might be.

Instead of viewing the file locally, run it through a local webserver. Two easy options are
XAMPP: http://portableapps.com/apps/development/xampp
Uniform Server: http://www.uniformserver.com/
Both require no installation. If you have Visual Studio or WebMatrix, you can also run it through Cassini or IISExpress.

It can be that you are using a VPN(Virtual private network) which analytics blocks. Try loading https://www.google-analytics.com/analytics.js
If id does not work try disabling the VPN and try again.
Or as someone else mentioned it could be that your AdBlock is blocking it.

Detect installed extensions in browsers?

Is it possible to detect via JS what extensions / add ons a user has installed on his browser? The use case was the a particular chrome extension, Autofill was setting some text values into hidden zip fields causing some validations to fail and I want to show a message to the user that this extension might create problems.

For Firefox: First snippet of code on: AddonManager.jsm - MDN
Components.utils.import("resource://gre/modules/AddonManager.jsm");
AddonManager.getAllAddons(function(aAddons) {
// Here aAddons is an array of Addon objects
});
// This code will execute before the code inside the callback
Must run this code in privelaged javascript, as in not a tab. You can try for specialPowers though I don't know how that works.
To run privelaged script from your site you will have to create a firefox addon and addEventListener's to your site, like a button to list the addons, you would attach a privelaged function to that.
With the addon you enable/disable addons, but users find that annoying because addons do some obtrsuvie stuff on install sometimes.

For Chrome extensions specifically, only certain extensions are detectable so this is not a very good method, but as far as I know, there are no longer any reliable methods to detect browser extensions.
For the extension that you want to detect, you would need its Extension Id and its Web accessible resource.
Some extensions have web accessible resources and some do not. If there is no web accessible resource, you will not be able to detect that extension.
To find the web accessible resource, you will need to look at the extensions chrome.manifestfile. It will tell you if there is web accessible content. For example, the chrome.manifest file might say:
content web-developer content/web-developer/ contentaccessible=yes
Generally, its not very effective to look for browser extensions since you have to know which extensions you want to detect ahead of time and many times they are undetectable.
Also, here's a good link that I used when I was trying to do the same thing here

NavigatorPlugins.mimeTypes
Take a peek at the MDN page
https://developer.mozilla.org/en-US/docs/Web/API/NavigatorPlugins.mimeTypes?redirectlocale=en-US&redirectslug=Web%2FAPI%2FNavigator.mimeTypes
Hope it helps

In JavaScript check to see if the zip field has been changed while it is hidden and show a warning to the user that an extension might be causing issues.

For Firefox you can do it with Mochitest/SpecialPowersAPI
https://developer.mozilla.org/en-US/docs/SpecialPowers

What is "chrome-extension://"

I found the some strange <script/> tags on a site:
<script src="chrome-extension://lifbcibllhkdhoafpjfnlhfpfgnpldfl/document_iterator.js"></script>
<script src="chrome-extension://lifbcibllhkdhoafpjfnlhfpfgnpldfl/find_proxy.js"></script>
...
I haven't been able to find much information on this, but I highly doubt this is actually related to Google Chrome since this site in particular is still using <table>s for layout, and the source in question was retrieved with curl not a graphical web browser.
So,
What on earth is this?
What is chrome-extension://
Why is it using lifbcibllhkdhoafpjfnlhfpfgnpldfl as a directory name
Why is it pretending to be valid URL to a javascript file?
Why would I need find_proxy or document_iterator
Solved. As far as I know...
chrixian was right, It seems that only on this and a few select other pages, someone had re-saved them from Chrome's source-view with the Skype extension installed.
Thanks everyone for all your help, +1's for all! enjoy!

That is actually Skype Click to Call chrome extension.
Manage and view it using this link
chrome://extensions/?id=lifbcibllhkdhoafpjfnlhfpfgnpldfl

If you are using cURL to get the page, you're getting the HTML as it exists on the server--so I think a safe assumption would be: the author of the page initially saved the page from Chrome, he had an extension installed that inserted these script tages and lastly he didn't remove the script tags for one reason or another before putting the page on the server.

This is added by chrome as the page loads, to inject the extension's Javascript code into the page, so it can access the HTML document.

The Skype extension causes it by inserting all kinds of junk in webpages that you visit.
Do you have the Skype browser extension installed for Chrome?
Just disable the extension.

Chrome, like Firefox, provides developers with an easy API to extend the functionality of the web browser without needing to actually download and build the browser to do so.
They also provide a robust delivery system. In Google's case, it's the Google Chrome Web Store.
Extensions are installed locally on your computer, and use long strings as directory names to reduce the risk of collisions with another extension. In other words, if you and I both named our extensions "mycoolextension", then there would be a problem if a person tried to install your extension and my extension. The long string helps prevent collisions such as this.
The chrome-extension:// protocol is used by the browser to make requests to these local resources. Chrome extensions are developed using HTML5, JavaScript, and CSS, along with an API exposed to allow the local JavaScript to perform actions it would not normally be able to do on the Internet.
When you see these in the Chrome developer tools, it's just the extension doing it's thing, whatever that may be.
If you're seeing these, then you likely installed some extensions from the Chrome Web Store. To view them, go to the Tools menu and select "Extensions". This will show you a list of all installed Chrome extensions and apps.
To learn more about extension development, see the Getting Started Tutorial.
Also, as someone else mentioned, you're using the Skype Call Extension. However, an app using that directory name doesn't appear in the first page of the search results. It might be worth doing some more research to make sure you got that extension from a legitimate source, whether that be Skype or the Chrome Web Store.
If you're seeing it in Chrome developer tools for every request you make, it means it has access to all your websites, which could be benign, like if they're just making phone numbers clickable, or it could be malicious, if it's scraping your bank account info and shipping it off to some third party server. :)

It's a Chrome extension, and chrome-extension:// is a URL for extensions to address their contents via Javascript.
lifbcibllhkdhoafpjfnlhfpfgnpldfl is the unique identifier for the extension. I can't find it with a search, but apparently it might be Skype.
It's not pretending... it is a valid URL. The Javascript file is located in the extension. If you were to look on your harddrive you'd probably find that very file in the extensions folder.
The functions its calling probably are some sort of detection used by the extension to see if it needs to enable itself.
See this for some additional information:
Checking if user has a certain extension installed