Have you noticed the same ads showing up in different places? Have you had the sneaky feeling you’re being watched? You mention something on your phone, then ads start showing up for that? Welcome to the connected world!
This from Kirk McElhearn
The advertising identifier on an Apple device does not identify you personally, but it can be used by advertisers to create a profile about you. If it’s never reset, that profile increases in detail, allowing advertisers to target ads to you based on your Internet activity.
Mozilla’s point is that resetting this identifier prevents advertisers from developing rather detailed profiles on users, and is simple to do. It’s not a hardware identifier (such as the EMEI of your iPhone), but rather a number generated by your operating system.
However, you can manually reset this advertising identifier, and it’s a good idea to do so regularly. Here’s how.