I wasn’t sure if this belonged in Meta, but I suppose General should be fine. Perhaps I should just tag @beschizza .
Embedded Vimeo videos in blog view have never displayed correctly in Firefox.
Examination of the HTML reveals:
<div class="embed-vimeo" style="text-align: center;">
Removing the “style” tag in this case fixes the problems.
(I should double-check to see if that long-standing Vimeo autoplay bug has been fixed now.)