Searching for answers about ways to record Firefox passwords in Gnome Seahorse Keyring vault,
I found severals possibilities:
Firefox Gnome Keyring firefox addon
from https://github.com/ in this answer and this answer
Gnome keyring password integration firefox addon
from https://addons.mozilla.org/en-US in this question
Integration con Gnome Keyring firefox addon
from https://addons.mozilla.org/fr
seems to be the Spanish version of the previous bullet on the French server (humm weird)
add this PPA in https://launchpad.net and install package called "mozilla-gnome-keyring"
from this bugzilla