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?
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.
The other thing I can think of is that you may be using Firefox from snap or flatpak and not a native package. These often have problems with system integration and native notifications are one example of this.
sorry 'ugly' is not the correct word, but if you notice these notifications are just firefox's windows (you can see it in the process bar on the left), so are not real notifications coming from your OS notification center
however I don't know what happend, but today they fixed themselves... this is how they look like now:
I don't know what happened, I didn't even updated anything, I just enabled and disabled some settings, reinstalled libnotify and rebooted a few times