ubuntu_ imposible to update firefox 9 to firefox 10

Until very recently, it has been relatively easy to update Firefox. [I am running Maverick Meerkat / Ubuntu 10.10]. But updating Firefox 9.0.1 to Firefox 10 is far more tricky. Here is the message I get each time I try: W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ maverick/partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_maverick_partner_binary-i386_Packages) W: Duplicate sources.list entry http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt/ all/main i386 Packages (/var/lib/apt/lists/downloads.sourceforge.net_project_ubuntuzilla_mozilla_apt_dists_all_main_binary-i386_Packages) Any suggestion welcome if anybody has found the way to FIX THIS!!!