I'm trying tu use this extension.
phpBB version 3.1.10, Safari 11.1.1, MacOS High Sierra.
I can attach the mp3 file, insert in my message, then the player bar appears in the message body.
Then if I click the play button, I can hear the mp3 but my user gets logged out of the forum ....

The bug doesn't affect Chrome browser, only safari.
Thanks