Why some applications sometimes become not “minimizable” on OS X?

Question

Sometimes for unknown circumstances to me, some applications (like Firefox) lose the minimize button.

What might the cause be?

Answer 1

I am not sure myself but a quick Google search reveals some interesting theories:

From MacRumors:

For some reason the OS seems to get disconnected from the Dock and disables the minimization. I haven't found a cause yet but I usually find that opening /Applications/Utilities/Terminal.app and running: Code:

killall -HUP Dock

fixes it. The only downside is that all windows which are currently having issues will not suddenly start working but all new windows will behave properly.