You can learn a lot about a site when you monitor its network connections when you connect your browser to it.
You may see connections to third-party sites, ads, web analytics scripts and a lot more just from that.
These resources are often essential for a site's functionality, and blocking them may break part or all of a site.
There are two concerns that Internet users may have when it comes to the use of these content delivery networks: privacy and speed.
Speed is easier to explain. While it is often faster to use a CDN for resources than a locally hosted version on the site's server itself, it still means having to make a connection to the CDN in first place. That's not as fast as making these resources available locally on the user's computer.
Privacy, because connections to these sites are made, and these sites may drop cookies on your local system. They may also record your Internet activity since you connect to them using a web browser, and get information out of those connections such as your operating system, the web browser you are using, your IP address or location in the world.
Decentraleyes for Firefox takes care of both of those, at least for selected content delivery networks and resources.
- Supported CDNs: Google Hosted Libraries, Microsoft Ajax CDN, CDNJS (Cloudflare), jQuery CDN (MaxCDN), jsDelivr (MaxCDN), Yandex CDN, Baidu CDN, Sina Public Resources and UpYun Libraries.
- Resources that come bundled with the extension: AngularJS, Backbone.js, Dojo, Ember.js, Ext Core, jQuery, Modernizr, MooTools, Prototype, Scriptaculous, SWFObject, Underscore.js and Web Font Loader.
The extension blocks connections to these content delivery networks by replacing the requests with resources loaded locally.
This takes care of both issues. Locally loaded resources are always faster than remotely loaded resources, even if a powerful fast network makes them available on the Internet, and since connections are not made anymore to these networks, there is no privacy impact as well.
Decentraleyes is a new extension, and I wish it would do more than what it is offering right now. First, it is difficult to tell whether a resource was replaced or not. It would be great if this would be highlighted in form of a log or even an icon that highlights the number of resources replaced with local resources.
Second, it works only if supported resources are loaded. There are however a multitude more resources that may get loaded from content delivery networks. An option to add your own replacements would be useful.
Third, it should not necessary limit its functionality to CDNs. Sites may load these resources from their server, and while you won't get any privacy improvements blocking it and replacing it with a local one, you may get loading speed improvements.
Decentraleyes is a good extension that introduces something that nothing else offered before. It could become a great extension if its author would improve it further. (thanks Tom)