Firefox 56 doesn't run any plugins other than Flash. The only version that runs other plugins is the Extended Support Release (ESR) of Firefox 52. (Plugins are different from extensions, but extensions designed to install plugins also no longer work.) ESR was first developed to meet the needs of large organizations that wanted Firefox to change much more slowly, but anyone can run it. It will retain the features of Firefox 52 and get regular security updates through around next June. More information on this change and ESR: [[Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work?]]