Why the master password window is opening when there is already one?

Everytime I start a Firefox window the first time there is a certain delay, after the the delay Firefox ask me for my master password. That's fine! But if I start Firefox and move to a website which require a password which is stored in the Firefox password manager before the end of the delay, Firefox ask me instant for the master password. The problem is, if I start to enter my master password it often happens, that at the end of the first mentioned delay and in my writing process a second window with the master password opens. Isn't it possible to deactivate the second master password window if there is already one? Would love that feature and would improve my usability experience. Thank you so much, for what you do! Richard