Tested in Firefox (41), and Firefox Nightly (44.0a1) under up-to-date Linux with Skia.

This breaks for me when the viewport is higher than its width, which is how I normally have it. It breaks by not drawing the head and only drawing the bits that overlay the eyes.

Also getting some warnings in the console, unsure if it's due to the site or the browsers implementaion:

PROGRAM_INFO_LOG: warning: sampler arrays indexed with non-constant expressions is forbidden in GLSL 110 warning: Variable sampler array index unsupported. This feature of the language was removed in GLSL 1.20 and is unlikely to be supported for 1.10 in Mesa. warning: Variable sampler array index unsupported. This feature of the language was removed in GLSL 1.20 and is unlikely to be supported for 1.10 in Mesa. [···] repeats