I tested the speedhack on Cheat Engine on both Firefox and Internet Explorer.

Strangely, Internet Explorer is a lot more stable because; On firefox, sometimes it goes on strange slow down intervals (Like from fast to slightly slower and even slower than normal then back to fast and so on) and it even stutters. Internet Explorer doesn't do that, it's as fast as it can be (only gets a little bit slow on demanding areas, so to say).

Don't really want to change my browser, still want to use FireFox because of the badass addons, so anyone perhaps got any tweak or so to stabilize FireFox's shitty speedhack "support"?

Thanks for the help, I did search for some solutions and tweaks, the one about the add-ons seemed to be common, thought that wasn't my problem; I always check and remove (not disable) the addons I don't use, I even tried Firefox without any addons and the games were still unstable with that speedhack.

Didn't try the one about scripts, but I suppose "AdBlock Plus" somehow does that, right? Other than that I don't think the scripts were the culprit.

So, I just realized that the problem was a tweak that I guess it was supposed to apparently speed it up; Disable protected mode. I removed that "ProtectedMode=0" tweak, so now it is "protected", and it is fast. Kind of ironic considering this thing actually slows you down.