Please keep in mind that these numbers are not 100% accurate. We do the best we can to parse out the add-on version check pings that this number is based on, but what we don't do is systematically attempt to track users. That means we don't have a cookie that we can rely on to determine exactly how many users are using a particular add-on. We can only count the number of pings.<p>Firefox will ping for a version check multiple times during the process of a browser upgrade. The user can manually check for updates as many times as they like. There are weird mis-configured proxies that can spam a single ping a hundred times for some reason, and there are browsers that have been recompiled for a variety of reasons that can behave in a non-standard fashion.<p>In each of these cases, we do the best we can to eliminate spurious or duplicate requests, but because of NAT and DHCP, we can't really rely much on an IP address to determine the validity of a set of requests.<p>Personally, I'm happy to provide less accurate statistics and be able to feel good that I am not violating Firefox users' privacy. This extends down to things such as not even storing IP addresses in our data warehouse once the access log data has been parsed. Regardless of the fact we have privacy policies that state we won't do anything bad with the data, I prefer to not even have the data available in a database at all.