It's kinda hard to explain but after a full Cleaninstall of windows the error was persistent.
If I freshly opened Firefox and go to a YouTube video the effects are powerful noticeable and "like it's supposed to be" but going to a second video, pausing the video or even reloading the same video with F5 the effects loose their "power". I can only reset this by completely restarting Firefox and then again only for one video where I can't even jump to my last view time cause it will loose it again...
To note here is that switching nahimic off and on still has a difference in sound but not the (like I said even if it sounds wrong) "power" it has if I restart Firefox.
Firefox 55.0.03 (64bit)
Windows 10 1703 (15063.540)
MSI GT72-2QD (5GEN)