Android Firefox and Chrome both implement the floating-point textures extension, but your devices GPU also has to natively support it.

If you're interested, you can check what your device supports with a tool like this: https://play.google.com/store/apps/details?id=com.darkrockst...

Not all of the GLES extensions will be exposed to WebGL, but most WebGL extensions directly map to a GLES one (GL_OES_texture_float in this case).