It is my understanding that it's an either/or thing with the proprietary nvidia drivers and mesa. On some systems, the openGL portions of each may actually conflict.
See what the output of the following command is:
Code:
LIBGL_DEBUG=verbose glxinfo | grep -iE "opengl|^direct|^libgl"
That assumes the glxinfo binary is installed. Depending on the distro, it might be provided by the mesa package (or maybe mesa-utils). On my Arch system, it's provided by mesa-demos.