Both Panasonic FX48 and Fujifilm X100 have 12.0 MP resolution sensors but Panasonic FX48's sensor is 1/2.3" (6.08 x 4.56 mm ) and Fujifilm X100's sensor is APS-C (23.6 x 15.8 mm ).
Since Fujifilm X100's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Panasonic FX48.
One other difference between these two cameras that is worth mentioning is that Fujifilm X100's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the FX48 and X100 sensor size comparison.
As seen above, Fujifilm X100 has a 13.5x Larger sensor area than Panasonic FX48. 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.