Does not show up for WAV files

[LinAGKar]

The Open in Browser dialog does not seem to show up for WAV files, e.g. the links at https://www.rowetel.com/wordpress/?page_id=452, instead those go straight to Firefox' download dialog.

[Rob--W]

Even if I save the .wav file locally, I cannot open it directly in Firefox.

The extension cannot get Firefox to view something inline if Firefox doesn't support viewing it.
This bug needs to be fixed first: https://bugzilla.mozilla.org/show_bug.cgi?id=1247826