So I searched for and turned off/blocked every tweak option I could find that was related to media. I didn't want it playing, I didn't want it visible or referenced. Hell, I didn't even want any part of it to load at all. I disconnected all of it.
All makes sense..but the prefs file I use is one I adjusted myself - simply because yours was so economical it broke a lot of sites.
On mine I didn't make any adjustments that effect media playback (not knowingly) so not sure of the issue - not a problem really as QTE is not a workable solution for me.