The exception was with Firefox 51.0.1, I just tried again and it happened at the same moment, I think it is when the enemy is defeated that the exception triggers.
I have this in the log:
Error: WebGL: blendEquationSeparate: modeRGB: invalid enum value MAX 2d2555a2-791c-4860-8c53-09a13266c295:1:196538
Error: WebGL: No further warnings will be reported for this WebGL context. (already reported 32 warnings) 2d2555a2-791c-4860-8c53-09a13266c295:1:196538
rekt
2d2555a2-791c-4860-8c53-09a13266c295:1:189016
Pseudo Tracepoint: Damage being modified