User wrote a custom shader for particles. I use distance() to measure a pixel's UV distance with the particle center. This works fine in editor, and on PC and webplayer builds. However, it does not work in WebGL (Firefox 41.0.2). Replacing the calculation with length() works.

Repro:
--Open the Main.unity scene and play it in the editor
--you should see the white particles
--Make a WebGL build
--play it in browser
--NOTICE that the particles are not rendering and no error or warning is thrown

The problem seems to be in shader code that does "distance(uv, float2(0.5,0.5))", with uv being a float4 - hlsl2glsl shader translator picks a float4 overload, whereas actual HLSL compiler picks a float2 overload. Changing code to "distance(uv.xy, float2(0.5,0.5))" fixes the issue.