Here's a larger part of glxinfo:
name of display: :0.0
display: :0 screen: 0
direct rendering: Yes
server glx vendor string: NVIDIA Corporation
server glx version string: 1.4
server glx extensions:
GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_SGIX_fbconfig,
GLX_SGIX_pbuffer, GLX_SGI_video_sync, GLX_SGI_swap_control,
GLX_EXT_swap_control, GLX_EXT_texture_from_pixmap, GLX_ARB_create_context,
GLX_ARB_create_context_profile, GLX_EXT_create_context_es2_profile,
GLX_ARB_create_context_robustness, GLX_ARB_multisample,
GLX_NV_float_buffer, GLX_ARB_fbconfig_float, GLX_EXT_framebuffer_sRGB
client glx vendor string: NVIDIA Corporation
client glx version string: 1.4
client glx extensions:
GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_visual_info,
GLX_EXT_visual_rating, GLX_EXT_import_context, GLX_SGI_video_sync,
GLX_NV_swap_group, GLX_NV_video_out, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer,
GLX_SGI_swap_control, GLX_EXT_swap_control, GLX_ARB_create_context,
GLX_ARB_create_context_profile, GLX_NV_float_buffer,
GLX_ARB_fbconfig_float, GLX_EXT_fbconfig_packed_float,
GLX_EXT_texture_from_pixmap, GLX_EXT_framebuffer_sRGB,
GLX_NV_present_video, GLX_NV_copy_image, GLX_NV_multisample_coverage,
GLX_NV_video_capture, GLX_EXT_create_context_es2_profile,
GLX_ARB_create_context_robustness
I suppose it could be not detected correctly because it's reported as a client glx extension? [Err no, that's not it...]