Mozilla is excluding Flash from a more general clamp-down on the enablement of browser add-ons with the latest edition of Firefox.
Firefox’s click-to-activate plugin whitelist, introduced in September 2013, has been removed.
This means that users will have to proactively enable add-ons while surfing using Firefox 47.0 beta and subsequent releases, with the single exception of Flash. The hacker favourite will still run by default, at least for the next few releases.
Firefox 53 is due to ditch plug-in support for Flash in favour of more modern (and safer) web technologies, according to a third-party Firefox compatibility site.
Firefox developers discuss the implications of requiring users to enable plug-ins in order to use them (with the exception of Flash) in a thread on the BugZilla developer forum, here.
Mozilla is already preparing for a post-Flash world. Firefox 53 beta (release notes here) will play embedded YouTube videos with HTML5 video if Flash is not installed.
Google ordered almost all ads to adopt HTML5 back in February in a move akin to serving Flash with a one-way ticket to the knackers' yard. ®