Why are firefox notifications so ugly?

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