Do you mean they don't activate? Maximize implies something that doesn't really happen at all in OS X.
If you mean activate, does the app become active, noted by the menu bar changing to relect the application's menus? If so, are the windows in another desktop?
They are already running. When I say 'maximize' what I mean is when I click on the dock icon(eg. Firefox) the application does not display. And yes the menu bar does change to the application(ie. Firefox) but the window does not display.
I do have multiple desktops but when clicking on Firefox would it not switch to desktop and then display Firefox window?