In some of the binary packages compiled from www-client/firefox-128.4.0-r1 the lto-useflag is still mentioned in the USE file (in metadata.tar.xz). This use flag has been removed from the 128.4.0-r1 ebuild. So these binary packages can never be used in an emerge, because a non-existing use-flag cannot be selected.
That's just because they weren't revbumped to drop the flag. There's nothing that can really be done about that.