HTML5-Audio-tag not playing in Firefox

Question

I want to use audio-tags to play opus-files:

<audio controls>
  <source src="espeak.opus" type="audio/ogg">
    Your browser does not support the audio element.
</audio>

Works locally but with Firefox it does not work on the server: https://tools.wmflabs.org/tts-comparison/

I've set the mimetypes, and also tried Ogg-Vorbis. (opus and Ogg-Vorbis are both supported by Firefox). Works in Chrome.

What am I missing?

Answer 1

Turned out it was Ublock blocking the players…