Over the last decades, the Free/Libre/Open Source Software (FLOSS) phenomenon has been a topic of study and a source of real-life artifacts for software engineering. A FLOSS project usually has a community around its project, organically producing informative resources to describe how, when, and why a particular change occurred in the source code or the development flow. Therefore, when studying this kind of project, collecting and analyzing texts and artifacts can promote a more comprehensive understanding of the phenomenon and the variety of organizational settings. However, despite the importance of examining Grey Literature, such as technical reports, white papers, magazines, and blog posts for studying FLOSS projects, the Grey Literature Review is still an emerging technique in software engineering studies, lacking a well-established investigative methodology. To mitigate this gap, we present and discuss challenges and adaptations for the planning and execution of grey literature reviews in the FLOSS scenario. We provide a set of guidelines and lessons learned for further research, using as an example a review we are conducting on the Linux kernel development model.