Back in September, Mozilla made an announcement:
This week Mozilla joined Open Invention Network as a licensee. OIN is an organization which helps protect the Linux ecosystem by building a variety of defenses against patent attacks. These defenses include both traditional mechanisms, like defensive patent pools, and more innovative approaches, like the Linux Defenders project, which uses a variety of methods to proactively prevent the publication of particularly egregious patents. As a licensee, we’ll have access to OIN resources in case we’re threatened by operating entities with patents, and over time we’ll likely become more involved in providing our own ideas and resources to OIN projects.
On Open Enterprise blog.