Last month, Forbes started blocking ad blocker users from accessing the site. While it sounds easy, however, there are many technical “gotchas” that publishers need to watch out. For example, in this case, Forbes still blocked this user even she already turned off her Adblock Plus plugin on FireFox.
The Lesson
The most common problem I’ve seen is inaccurate ad-block checking. There are many ad blockers, and they behave differently. Even the same ad blocker plugin don’t share the same behaviors on different browsers. Therefore, things can get complicated quick.
In this example, it is because of FireFox built-in privacy protection messing up Forbes’s code. Always test your detection engine before rolling it out.
Note: This bug might already be fixed by the time you read this article.