We have introduced a code of conduct. This change only codifies our existing rules, for any newcomers to read. All users are expected to abide by them.
This page is for the original 2011 game. For the 2014 remake, see The Binding of Isaac: Rebirth.
On the options menu, it states F is the key you use to toggle fullscreen/windowed mode. However, this only works on the title menu or in the pause menu. In-game, pressing F does absolutely nothing unless the game is paused. Currently, there is no fix for this.
A fan made fix has been developed to solve this issue on Windows.
For the achievements gained on OS X to be unlocked in Steam, one has to copy and replace the so.sol files as outlined here. The file is located in:
~/Library/Preferences/Macromedia/Flash Player/#SharedObjects/''<Random String>''/localhost/
After extracting it, follow the instructions given in the aforementioned link. Finally launch the game and see the achievements unlock.
Solution: press F, it toggles fullscreen.