I have decided to test out using Safari as my main browser as opposed to Google Chrome. In order to do this I needed to assign it to a single desktop. However, when I tried to do this, I found that the mission control desktop selection options were absent, as shown in the attached screenshot. As "Safari is essential to Mac OS X" it cannot be deleted, preventing me from replacing it to see if this is related. Has anyone encountered this before? I previously had it set to "all desktops" and on others Macs the options are present.