Firefox (any version) + Greasemonkey + Youtube HTML5

[smoovi]

Okay, so here's my problem which I have been googling for slightly 2 years now without finding any solution whatsoever. Every single instance of Firefox in combination with any version of Greasemonkey including all the Nightly builds/dev versions and even different forks like Waterfox are causing this problem - even with different combinations of mainboards + CPUs or different graphics cards that I had in my system with fresh Windows 7 installations I was able to recreate this problem.

Now the problem description: Using the HTML5 version of Youtube with or without Adobe Flash (any version) being installed while having the Greasemonkey addon (with or without any actually installed scripts for GM) causes the video to be played for 1-2 seconds and then continue to play while after said 1-2 seconds another instance is being played where only the audio is being played. Then another instance and another until my RAM is completely full and my computer stops responding unless I quickly after starting the video and hearing the additional videos being played go back to a different site or close Firefox altogether.

To make it more clear, it happens like that: I start the video, the video is playing and the sound is playing in sync. Then the same sound starts playing 1-2 seconds after and overlaps with the already played sound, then 4-5 seconds later another sound starts playing and it continues over and over again until you can hear about 50+ different instances of the same video sound running in the background at the same time. At around 15-20 seconds I can still see the video playing but I can hear the sound of multiple videos playing as if I opened them 10 times in a row in different browser windows 1-2 seconds apart from each other (wich I obviously didn't).

Does anyone know how such a problem could even exist over such a variety of different hardware and software configurations? What could be the cause of this? Yes, I've disabled every addon except Greasemonkey and yes, I've tried multiple versions of Firefox and Greasemonkey, just to make it clear once again. If I disable Greasemonkey, everything works totally fine and with or without Greasemonkey I am not having the same problems with Adobe Flash being active or installed.

[therube]

What version of GM?
Greasemonkey Version History

Does the same happen in a new, clean Profile with only GM extension (itself, no scripts) installed?

[smoovi]

What version of GM?
Greasemonkey Version History

Does the same happen in a new, clean Profile with only GM extension (itself, no scripts) installed?

Yes it does. Also, the version of Greasemonkey is irrelevant as it happend on multiple different versions. My current version is 3.6. I've tried using the beta versions but there hasn't been any change. Yes, it happens with just the GM extension installed. As soon as I install Greasemonkey new on a fresh installation of Firefox the problem occurs.