What does the "Logout Required" message on this update mean? Is it referring to Firefox sync, the websites you're > logged into, or something else?
It's not good idea to update Firefox when it's already running (although it's possible). So you can read "Logout Required" as "quit all your running firefox instances before the update".
Not good Adobe Flash Player not working on this version firefox after i back to firefox-55.0.3-1.fc26 flash player working ok firefox-56.0-3.fc26 have same problem like firefox-56.0-2.fc26
I'd actually consider that as a good feature. Anyway, you can fetch your own security hole at https://koji.fedoraproject.org/koji/buildinfo?buildID=979704 when it completes.