Ever been frustrated because the Q key only cycles between the Viewer & the Canvas, but you're currently in the Browser so the Q shortcut won't work? Why not use the Mac OS shortcut Cmd+Shift+Tilde. This will cycle not only through the four main windows in FCP, but all the windows yo have open in the program.
On my dual monitor setup, I have the Timeline, Viewer & Canvas on one monitor and on the other monitor I have the Browser covering the Scopes Window. By using Cmd+Shift+Tilde I can quickly switch between the Browser & the Scopes window as well as the four main windows. As Cmd+Shift+Left Square Bracket cycles through window tabs to the left, substituting the left bracket for the tilde key switches from Scopes to the Mixer window.
Cmd+Shift+Tilde is useful as it cycles through the windows in any Pro App applications you may be in, as it is a generic OS command. You should be able to change this command to the F13 key, but
this is not working on my system on OS 10.4.11.
Dave