OS X Mountain Lion: If you can’t change the font size
If you don’t see a way to change the font size in the Fonts window, the size controls are hidden.
- Open the Fonts window in your apps by choosing Format > Font > Show Fonts or Format > Show Fonts.
- Choose Edit Sizes from the Action pop-up menu (looks like a gear) in the lower-left corner of the Fonts window.
To make a list of font sizes appear in the Fonts window, select Fixed List.
To make a font size slider appear in the Fonts window, select Adjustable Slider.