Someone asked this a while ago. It was OpenGL related.
You can try to see what's going on with:
LIBGL_DEBUG=verbose ubuntu-mate-welcome
What works for some is forcing software rendering.
LIBGL_ALWAYS_SOFTWARE=1 ubuntu-mate-welcome
That way OpenGL 3.0 is emulated with the Mesa library. I'm not sure if it's related to OpenGL version or if it's some bug in WebKit2 which is used for this application. Those cards Nvidia fx 5200 and ati radeon 9200 use older version of opengl.
You can check with
glxinfo | grep -i "opengl"
And with enabled software rendering
LIBGL_ALWAYS_SOFTWARE=1 glxinfo | grep -i "opengl"