Firefox продолжает устанавливать выпуск разработчика, а не версия 48

Я плохо знаком с Ubuntu, и я пытался следовать инструкциям установки Firefox Developer Edition, но это продолжает устанавливать Firefox 48.

sudo add-apt-repository ppa:ubuntu-mozilla-daily/firefox-aurora
sudo apt-get update
sudo apt-get install firefox

Это шаги, которые я делал. Я просто получаю сообщение, говоря, что Firefox уже является последней версией.

Однако, когда я делаю следующий, я вижу, что версия 50.0 доступна в списке

   sudo apt-cache madison firefox

firefox | 48.0+build2-0ubuntu0.14.04.1 | http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
       firefox | 48.0+build2-0ubuntu0.14.04.1 | http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
       firefox | 28.0+build2-0ubuntu2 | http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
       firefox | 28.0+build2-0ubuntu2 | http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
       firefox | 28.0+build2-0ubuntu2 | http://us.archive.ubuntu.com/ubuntu/ trusty/main Sources
       firefox | 48.0+build2-0ubuntu0.14.04.1 | http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main Sources
       firefox | 48.0+build2-0ubuntu0.14.04.1 | http://security.ubuntu.com/ubuntu/ trusty-security/main Sources
       firefox | 28.0+build2-0ubuntu2 | http://archive.ubuntu.com/ubuntu/ trusty/main Sources
       firefox | 50.0~a2~hg20160909r333109-0ubuntu1~umd1~trusty | http://ppa.launchpad.net/ubuntu-mozilla-daily/firefox-aurora/ubuntu/ trusty/main Sources

Будучи в новинку для этого, я предполагаю, что делаю что-то не так или неправильно понимаю что-то. Можно ли помочь?Спасибо.

Править

Политика кэша Кв. произвела:

apt-cache policy firefox
firefox:
  Installed: 48.0+build2-0ubuntu0.14.04.1
  Candidate: 48.0+build2-0ubuntu0.14.04.1
  Version table:
 *** 48.0+build2-0ubuntu0.14.04.1 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     28.0+build2-0ubuntu2 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

политика способного кэша

Package files:
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     release a=now
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     release v=14.04,o=LP-PPA-ubuntu-mozilla-daily-firefox-aurora,a=trusty,n=trusty,l=Firefox Aurora builds,c=main
     origin ppa.launchpad.net
 500 http://ppa.launchpad.net/ubuntu-mozilla-daily/firefox-aurora/ubuntu/ trusty/main amd64 Packages
     release v=14.04,o=LP-PPA-ubuntu-mozilla-daily-firefox-aurora,a=trusty,n=trusty,l=Firefox Aurora builds,c=main
     origin ppa.launchpad.net
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     origin oem.archive.canonical.com
 500 http://oem.archive.canonical.com/updates/ trusty-oem/public amd64 Packages
     release v=14.04,o=Canonical,n=trusty-oem,c=public
     origin oem.archive.canonical.com
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     origin oem.archive.canonical.com
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     origin dell.archive.canonical.com
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     origin dell.archive.canonical.com
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     origin dell.archive.canonical.com
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     origin dell.archive.canonical.com
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     release o=Node Source,n=trusty,l=Node Source,c=main
     origin deb.nodesource.com
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     release o=dotnet-release trusty,a=trusty,n=trusty,l=dotnet-release trusty,c=main
     origin apt-mo.trafficmanager.net
 500 http://extras.ubuntu.com/ubuntu/ trusty/main i386 Packages
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     origin extras.ubuntu.com
 500 http://extras.ubuntu.com/ubuntu/ trusty/main amd64 Packages
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     origin extras.ubuntu.com
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 500 http://security.ubuntu.com/ubuntu/ trusty-security/restricted amd64 Packages
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 100 http://us.archive.ubuntu.com/ubuntu/ trusty-backports/restricted i386 Packages
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 500 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main i386 Packages
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     origin us.archive.ubuntu.com
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 500 http://us.archive.ubuntu.com/ubuntu/ trusty/multiverse Translation-en
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 500 http://us.archive.ubuntu.com/ubuntu/ trusty/universe i386 Packages
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Pinned packages: