All you really need to know
"Local content caching" is an optional feature in AdBlock for Chrome and Firefox. It allows your browser to get some of the information it needs to show you a web page from the AdBlock extension on your computer instead of from a server far away.
Local content caching provides a couple of important benefits.
- Bandwidth savings and faster load times. Some of the most commonly used web software libraries (web page "building blocks") are pulled directly from the AdBlock extension on your computer, avoiding the need to download that information from the Internet. That leaves more bandwidth for other purposes (say, streaming a video while you're uploading photos to Facebook) and pages load faster.
- Privacy protection. Many of the servers that deliver common web software libraries to your browser are owned by big technology companies such as Google, Amazon, and Microsoft. These companies can learn a lot about you by tracking your browser's requests for information. Local content caching "short-circuits" some of those requests, making it harder for companies to create a profile of you based on your online activities.
So, summing up, how do you know whether to turn on local content caching? For most people in most circumstances, there is no reason not to. We're making it an optional feature for now in case there are issues we haven't thought of. If you use a Chrome extension called HTTPS Everywhere, however, please see the note below.
How to turn local content caching on and off
The local content cache feature is an optional setting. To turn it on, click the AdBlock button in the browser toolbar, select Options, and on the GENERAL tab, select the checkbox next to Enable local content caching for popular website libraries.
A note about HTTPS Everywhere and local content caching
If you use a Chrome extension called HTTPS Everywhere, you might sometimes see an error that looks like this: "This extension failed to redirect a network request to  because another extension (AdBlock) redirected it to ." This is HTTPS Everywhere telling you it couldn't redirect an insecure request to HTTPS because AdBlock intercepted and redirected the request to its local content cache instead.
What should I do if I see this alert?
You can ignore it. The local content cache feature doesn't keep you from visiting a website you want to go to. It only affects software requests between computers.
This is what the alert looks like in versions of Chrome prior to Chrome 65:
This is what the alert looks like in Chrome 65 and later:
If you'd like to know more about content delivery networks (also called content distribution networks or CDNs) and our new local content cache feature, please read this post on AdBlock's Blog.