normcdn on "Firefox - Leave page or Stay"

Hi everybody,
I am using Firefox 49.0.2 to edit the title and description of all albums and images in my zenphoto gallery.
Is there a way to prevent Firefox to constantly displaying « This page is asking you to confirm that you want to leave - data you have entered may not be saved. Leave Page or Stay on Page » ? I understand the purpose of this, but I keep getting this message EVEN if I did not change anything.
Thanks