With the next release of three.js (R101), it’s possible to use a new type of render-target to solve this problem. WebGLMultisampleRenderTarget enables the support of multisampled renderbuffers. You can now perform “render-to-texture” and have an antialiasing render result. A post-process AA like FXAA is not necessary anymore.
Important: It’s required to use a WebGL 2 rendering context since multisampled renderbuffers is a WebGL 2 feature.