From FCKeditor Docs

Keystrokes

Keystrokes option determines what Keyboard Keystrokes will be use by the editor. First five keystrokes:

[ CTRL + 65 /*A*/, true ],
[ CTRL + 67 /*C*/, true ],
[ CTRL + 70 /*F*/, true ],
[ CTRL + 83 /*S*/, true ],
[ CTRL + 88 /*X*/, true ],

are browser keystrokes independent from FCKeditor functions and it is recommended not to change them. The other keystrokse are dedicated to FCKeditor functions. You may change or delete them.

Full Code:

FCKConfig.Keystrokes = [
[ CTRL + 65 /*A*/, true ],
[ CTRL + 67 /*C*/, true ],
[ CTRL + 70 /*F*/, true ],
[ CTRL + 83 /*S*/, true ],
[ CTRL + 88 /*X*/, true ],
[ CTRL + 86 /*V*/, 'Paste' ],
[ SHIFT + 45 /*INS*/, 'Paste' ],
[ CTRL + 88 /*X*/, 'Cut' ],
[ SHIFT + 46 /*DEL*/, 'Cut' ],
[ CTRL + 90 /*Z*/, 'Undo' ],
[ CTRL + 89 /*Y*/, 'Redo' ],
[ CTRL + SHIFT + 90 /*Z*/, 'Redo' ],
[ CTRL + 76 /*L*/, 'Link' ],
[ CTRL + 66 /*B*/, 'Bold' ],
[ CTRL + 73 /*I*/, 'Italic' ],
[ CTRL + 85 /*U*/, 'Underline' ],
[ CTRL + SHIFT + 83 /*S*/, 'Save' ],
[ CTRL + ALT + 13 /*ENTER*/, 'FitWindow' ],
[ CTRL + 9 /*TAB*/, 'Source' ]
] ;