Leica M9 has a
18.0MP Full frame (36 x 24 mm ) sized CCD sensor . On the other hand, Fujifilm X-Pro1 has a
16.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS I sensor and features EXR Pro processor.
Another similarity between these two cameras is that both Fujifilm X-Pro1 and Leica M9 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the M9 and X-Pro1 sensor size comparison.
As seen above, Leica M9 has a 2.3x Larger sensor area than Fujifilm X-Pro1. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.