By default, once a day both Firefox and Thunderbird will connect to the Mozilla server and update a list of blocked extensions and plugins in order to prevent you installing an unstable or dangerous plugin.
You can disable this feature by accessing about:config in Firefox or the advanced settings in Thunderbird and searching for “blocklist”. Double clicking extensions.blocklist.enabled will enable or disable it.
The host the software tries to access is addons.mozilla.org on port 443, HTTPS SSL. One of the IP addresses is 63.245.213.31.
