Comment # 9 on bug 1140184 from Wolfgang Bauer

(In reply to Stakanov Schufter from comment #8)
> Where can I force it to do this as "default" start settings, so to check if
> all is ok on the long run?
As I wrote earlier, you could add it to /etc/environment e.g., i.e. edit the
file in a text editor (as root) and in this case add the line:
MESA_EXTENSION_OVERRIDE="-GL_ATI_fragment_shader"

Or maybe add this line to ~/.profile:
export MESA_EXTENSION_OVERRIDE="-GL_ATI_fragment_shader"
(it will only affect your user account then)