The [NSFontPanel sharedFontPanel].styleMask == (NSTitledWindowMask | NSClosableWindowMask | NSResizableWindowMask | NSUtilityWindowMask)
. However, it shows resize indicators even if you add NSNonactivatingPanelMask
.
When you set [NSFontPanel sharedFontPanel].hidesOnDeactivate = NO
and activate another app, resize indicators stop working. This is by design, because even regular inactive windows cannot be resized.
So maybe you are trying to add resize indicators when the panel-owning app is inactive. Just a thought.