Some time ago I wrote a post explaining how to detect firefox add-ons. However, the described way only works for a couple of add-ons. And it doesn’t work for the most popular add-on of all called Adblock Plus. But instead there is an even simpler way to detect if a visitor coming to your website has activated Adblock Plus.
Since Adblock Plus blocks URLs and hides containers using a naming pattern (i.e. hiding all elements on a website containing the class “ad-column”) it is possible to trigger the add-on to hide an element on the page and then check with a simple JS-Script if it is still visible or hidden, the latter meaning that the visitor has Adblock Plus currently up and running.
Checking your Adblock Plus status…
The following script detects Adblock Plus by checking if the container with the id “adright” is hidden (using jQuery):
The script above works for the standard English filter subscription of Adblock Plus but might not be working for other country-specific subscriptions. For a complete overview of URLs and containers blocked by your filter subscriptions have a look at the filter rules in the Adblock Plus preferences and adjust the script accordingly.