Technic Launcher (minecraft) blank window on Gnome - openjdk 7 & 8

Hi there!
Whenever i open the Technic Launcher (java application) i get a blank window, it only happens on gnome.
I found the same problem online but couldnt figure how to solve it.
If anyone knows the solution i would like to know, thanks.

Online reading tell me that i have to set a “environment variable” to “_JAVA_AWT_WM_NONREPARENTING=1”, im just not sure where…

(EDIT)
I might just have found the solution: “_JAVA_AWT_WM_NONREPARENTING=1 XMODIFIERS= java -jar ~/Games/FTB/FTB_Launcher.jar”; i’ll try it when I get home