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About the "Non-power-of-two textures must have a wrap mode of CLAMP_TO_EDGE". If this is about the 2d texture material you can try setting ETC_CLAMP_TO_EDGE for TextureWrapU, TextureWrapV, TextureWrapW in first texture in IVideoDriver::getMaterial2D() and then set IVideoDriver::enableMaterial2D(true).
I guess if that's required we can try doing that by default somehow in the WebGL driver as well (maybe with size-check for texture). But I can only put this on todo for now for next year (or post Irrlicht 1.9 release as WebGL will still not be in there, sorry).