You are working on a high resolution retina screen; Fireworks does not support retina screens. Software that does support such screens will treat a group of 4 pixels as 1 pixel, and scale up the interface elements.
Since Fireworks is a dead application (development and support were halted over two and a half years ago in May 2013), this issue will NOT be rectified by Adobe. Fireworks and CS6 products are incompatible with retina screens on Windows.
However, the method described on this page may be able to fix your issue. Or it may not.