Hi,
I had a WebGL app running nicely in FireFox and Chromium (Ubuntu 12.10).
I upgraded from 12.10 to 13.4 (64bits).
Now it does not work correct any more in FireFox as well as Chromium).
No errors.
It still works correctly on other machines (ubuntu 12.04/FireFox, macBook/FireFox, windows/Chromium).
The bug turns up in the flowing lines of the vertex shader (coming from javascript)

Code:
uniform mediump vec3 criticalHeights;
attribute mediump  vec3 vertex;
...
if(criticalHeights[2] > vertex.z )
    {varAmbientLight = redAmbientLight; varDiffuseLight = redDiffuseLight;};
     }\n;"+
criticalHeights[2] and vertex.z vary between -100 and + a few hundred.
the 'if' statement always returns true, even with extreme values like -1000000.0 < vertex.z or criticalHeights[2] > 1000000.0
Thanks.


glxinfo:
name of display: :0
display: :0 screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
GLX_ARB_create_context, GLX_ARB_create_context_profile,
GLX_ARB_multisample, GLX_EXT_create_context_es2_profile,
GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info,
GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, GLX_OML_swap_method,
GLX_SGI_swap_control, GLX_SGIS_multisample, GLX_SGIX_fbconfig,
GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group, GLX_INTEL_swap_event
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
client glx extensions:
GLX_ARB_create_context, GLX_ARB_create_context_profile,
GLX_ARB_create_context_robustness, GLX_ARB_framebuffer_sRGB,
GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context,
GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_EXT_framebuffer_sRGB,
GLX_EXT_create_context_es2_profile, GLX_MESA_copy_sub_buffer,
GLX_MESA_multithread_makecurrent, GLX_MESA_swap_control,
GLX_OML_swap_method, GLX_OML_sync_control, GLX_SGI_make_current_read,
GLX_SGI_swap_control, GLX_SGI_video_sync, GLX_SGIS_multisample,
GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group,
GLX_EXT_texture_from_pixmap, GLX_INTEL_swap_event
GLX version: 1.4
GLX extensions:
GLX_ARB_create_context, GLX_ARB_create_context_profile,
GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context,
GLX_EXT_visual_info, GLX_EXT_visual_rating,
GLX_EXT_create_context_es2_profile, GLX_MESA_copy_sub_buffer,
GLX_MESA_multithread_makecurrent, GLX_MESA_swap_control,
GLX_OML_swap_method, GLX_OML_sync_control, GLX_SGI_make_current_read,
GLX_SGI_swap_control, GLX_SGI_video_sync, GLX_SGIS_multisample,
GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group,
GLX_EXT_texture_from_pixmap, GLX_INTEL_swap_event
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) 965GM
OpenGL version string: 2.1 Mesa 9.1.1
OpenGL shading language version string: 1.20
OpenGL extensions:
GL_ARB_multisample, GL_EXT_abgr, GL_EXT_bgra, GL_EXT_blend_color,
GL_EXT_blend_minmax, GL_EXT_blend_subtract, GL_EXT_copy_texture,
GL_EXT_polygon_offset, GL_EXT_subtexture, GL_EXT_texture_object,
GL_EXT_vertex_array, GL_EXT_compiled_vertex_array, GL_EXT_texture,
GL_EXT_texture3D, GL_IBM_rasterpos_clip, GL_ARB_point_parameters,
GL_EXT_draw_range_elements, GL_EXT_packed_pixels, GL_EXT_point_parameters,
GL_EXT_rescale_normal, GL_EXT_separate_specular_color,
GL_EXT_texture_edge_clamp, GL_SGIS_generate_mipmap,
GL_SGIS_texture_border_clamp, GL_SGIS_texture_edge_clamp,
GL_SGIS_texture_lod, GL_ARB_framebuffer_sRGB, GL_ARB_multitexture,
GL_EXT_framebuffer_sRGB, GL_IBM_multimode_draw_arrays,
GL_IBM_texture_mirrored_repeat, GL_3DFX_texture_compression_FXT1,
GL_ARB_texture_cube_map, GL_ARB_texture_env_add, GL_ARB_transpose_matrix,
GL_EXT_blend_func_separate, GL_EXT_fog_coord, GL_EXT_multi_draw_arrays,
GL_EXT_secondary_color, GL_EXT_texture_env_add,
GL_EXT_texture_filter_anisotropic, GL_EXT_texture_lod_bias,
GL_INGR_blend_func_separate, GL_NV_blend_square, GL_NV_light_max_exponent,
GL_NV_texgen_reflection, GL_NV_texture_env_combine4, GL_S3_s3tc,
GL_SUN_multi_draw_arrays, GL_ARB_texture_border_clamp,
GL_ARB_texture_compression, GL_EXT_framebuffer_object,
GL_EXT_texture_compression_s3tc, GL_EXT_texture_env_combine,
GL_EXT_texture_env_dot3, GL_MESA_window_pos, GL_NV_packed_depth_stencil,
GL_NV_texture_rectangle, GL_ARB_depth_texture, GL_ARB_occlusion_query,
GL_ARB_shadow, GL_ARB_texture_env_combine, GL_ARB_texture_env_crossbar,
GL_ARB_texture_env_dot3, GL_ARB_texture_mirrored_repeat,
GL_ARB_window_pos, GL_ATI_envmap_bumpmap, GL_EXT_stencil_two_side,
GL_EXT_texture_cube_map, GL_NV_depth_clamp, GL_APPLE_packed_pixels,
GL_APPLE_vertex_array_object, GL_ARB_draw_buffers,
GL_ARB_fragment_program, GL_ARB_fragment_shader, GL_ARB_shader_objects,
GL_ARB_vertex_program, GL_ARB_vertex_shader, GL_ATI_draw_buffers,
GL_ATI_texture_env_combine3, GL_ATI_texture_float, GL_EXT_shadow_funcs,
GL_EXT_stencil_wrap, GL_MESA_pack_invert, GL_MESA_ycbcr_texture,
GL_NV_primitive_restart, GL_ARB_depth_clamp,
GL_ARB_fragment_program_shadow, GL_ARB_half_float_pixel,
GL_ARB_occlusion_query2, GL_ARB_point_sprite, GL_ARB_shading_language_100,
GL_ARB_sync, GL_ARB_texture_non_power_of_two, GL_ARB_vertex_buffer_object,
GL_ATI_blend_equation_separate, GL_EXT_blend_equation_separate,
GL_OES_read_format, GL_ARB_color_buffer_float, GL_ARB_pixel_buffer_object,
GL_ARB_texture_compression_rgtc, GL_ARB_texture_float,
GL_ARB_texture_rectangle, GL_EXT_packed_float, GL_EXT_pixel_buffer_object,
GL_EXT_texture_compression_dxt1, GL_EXT_texture_compression_rgtc,
GL_EXT_texture_rectangle, GL_EXT_texture_sRGB,
GL_EXT_texture_shared_exponent, GL_ARB_framebuffer_object,
GL_EXT_framebuffer_blit, GL_EXT_framebuffer_multisample,
GL_EXT_packed_depth_stencil, GL_APPLE_object_purgeable,
GL_ARB_vertex_array_object, GL_ATI_separate_stencil, GL_EXT_draw_buffers2,
GL_EXT_draw_instanced, GL_EXT_gpu_program_parameters,
GL_EXT_texture_array, GL_EXT_texture_integer, GL_EXT_texture_sRGB_decode,
GL_OES_EGL_image, GL_MESA_texture_array, GL_ARB_copy_buffer,
GL_ARB_depth_buffer_float, GL_ARB_draw_instanced,
GL_ARB_half_float_vertex, GL_ARB_instanced_arrays,
GL_ARB_map_buffer_range, GL_ARB_texture_rg, GL_ARB_texture_swizzle,
GL_ARB_vertex_array_bgra, GL_EXT_separate_shader_objects,
GL_EXT_texture_swizzle, GL_EXT_vertex_array_bgra,
GL_NV_conditional_render, GL_ARB_ES2_compatibility, GL_ARB_debug_output,
GL_ARB_draw_elements_base_vertex, GL_ARB_explicit_attrib_location,
GL_ARB_fragment_coord_conventions, GL_ARB_provoking_vertex,
GL_ARB_sampler_objects, GL_ARB_seamless_cube_map,
GL_ARB_shader_texture_lod, GL_ARB_texture_rgb10_a2ui,
GL_ARB_vertex_type_2_10_10_10_rev, GL_EXT_provoking_vertex,
GL_EXT_texture_snorm, GL_MESA_texture_signed_rgba,
GL_ARB_get_program_binary, GL_ARB_robustness, GL_ARB_shader_bit_encoding,
GL_ANGLE_texture_compression_dxt3, GL_ANGLE_texture_compression_dxt5,
GL_ARB_internalformat_query, GL_ARB_texture_storage,
GL_ARB_invalidate_subdata

12 GLX Visuals
visual x bf lv rg d st colorbuffer sr ax dp st accumbuffer ms cav
id dep cl sp sz l ci b ro r g b a F gb bf th cl r g b a ns b eat
----------------------------------------------------------------------------
0x020 24 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x021 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x084 24 tc 0 32 0 r y . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x085 24 tc 0 32 0 r . . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x086 24 tc 0 32 0 r . . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x087 24 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 16 16 16 16 0 0 Slow
0x088 24 dc 0 32 0 r y . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x089 24 dc 0 32 0 r . . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x08a 24 dc 0 32 0 r . . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x08b 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x08c 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 16 16 16 16 0 0 Slow
0x06b 32 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None

24 GLXFBConfigs:
visual x bf lv rg d st colorbuffer sr ax dp st accumbuffer ms cav
id dep cl sp sz l ci b ro r g b a F gb bf th cl r g b a ns b eat
----------------------------------------------------------------------------
0x06c 0 tc 0 16 0 r y . 5 6 5 0 . . 0 0 0 0 0 0 0 0 0 None
0x06d 0 tc 0 16 0 r . . 5 6 5 0 . . 0 0 0 0 0 0 0 0 0 None
0x06e 0 tc 0 16 0 r y . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x06f 0 tc 0 16 0 r . . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x070 24 tc 0 32 0 r y . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x071 24 tc 0 32 0 r . . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x072 24 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x073 24 tc 0 32 0 r . . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x074 0 tc 0 16 0 r y . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x075 0 tc 0 16 0 r y . 5 6 5 0 . . 0 16 0 16 16 16 0 0 0 Slow
0x076 32 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x077 24 tc 0 32 0 r y . 8 8 8 8 . . 0 24 8 16 16 16 16 0 0 Slow
0x078 0 dc 0 16 0 r y . 5 6 5 0 . . 0 0 0 0 0 0 0 0 0 None
0x079 0 dc 0 16 0 r . . 5 6 5 0 . . 0 0 0 0 0 0 0 0 0 None
0x07a 0 dc 0 16 0 r y . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x07b 0 dc 0 16 0 r . . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x07c 24 dc 0 32 0 r y . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x07d 24 dc 0 32 0 r . . 8 8 8 8 . . 0 0 0 0 0 0 0 0 0 None
0x07e 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x07f 24 dc 0 32 0 r . . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x080 0 dc 0 16 0 r y . 5 6 5 0 . . 0 16 0 0 0 0 0 0 0 None
0x081 0 dc 0 16 0 r y . 5 6 5 0 . . 0 16 0 16 16 16 0 0 0 Slow
0x082 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 0 0 0 0 0 0 None
0x083 24 dc 0 32 0 r y . 8 8 8 8 . . 0 24 8 16 16 16 16 0 0 Slow