the last time I remember I received a firefox notification it was using the native notification (i'm using KDE, I also have the KDE integration addon) yesterday I received a notification from lemmy, and this is how they appear, in the center of the screen and... very ugly. what changed? is there a way to get back the native notification?
(you can check how your notification works here)
EDIT: in about:config page, alerts.useSystemBackend is set to true, but still it does not use the native notification
If libnotify package is not installed try installing it and see if it helps. I think I remember Gentoo warning about this in relation to notifications.