Firefox has started autoplaying videos. Previously, these were consistently being prevented from autoplaying, except for sites that I allowed.
It seems that Mozilla are migrating to a different autoplay configuration. There are now old, defunct, configuration options, replaced by undocumented and, in my opinion, unintuitive options.
It feels almost as if Mozilla is intent on having autoplay enabled, albeit in as nonintrusive a way as is deemed tolerable.
My own settings are shown below. They seem to block even the weird sites that game the browser to trick it into autoplaying (typically regional news sites).
I may try to document these systematically, one by one, to figure out exactly how each affects the browser, but I’ll first need to convince myself that life is not, in fact, too short!