安装任何稳定版本的 Firefox 软件包时我遇到错误：
逐步安装：
首先检查 Firefox 是否已安装：
$ firefox The program 'firefox' is currently not installed. You can install it by typing: sudo apt-get install firefox安装 Firefox：
Reading package lists... Done Building dependency tree Reading state information... Done The following extra packages will be installed: libcanberra0 libogg0 libstartup-notification0 libtdb1 libvorbis0a libvorbisfile3 libxcb-util0 xul-ext-ubufox Suggested packages: fonts-lyx libcanberra-gtk0 libcanberra-pulse The following NEW packages will be installed: firefox libcanberra0 libogg0 libstartup-notification0 libtdb1 libvorbis0a libvorbisfile3 libxcb-util0 xul-ext-ubufox 0 upgraded, 9 newly installed, 0 to remove and 29 not upgraded. Need to get 45.3 MB/45.6 MB of archives. After this operation, 113 MB of additional disk space will be used. Do you want to continue? [Y/n]y Get:1 http://ppa.launchpad.net/ubuntu-mozilla-security/ppa/ubuntu/ trusty/main firefox amd64 50.0+build2-0ubuntu0.14.04.1 [45.3 MB] Fetched 45.3 MB in 9s (4,880 kB/s) Selecting previously unselected package libtdb1:amd64. dpkg: warning: files list file for package 'firefox-mozilla-build' missing; assuming package has no files currently installed (Reading database ... 94637 files and directories currently installed.) Preparing to unpack .../libtdb1_1.3.8-0ubuntu0.14.04.1_amd64.deb ... Unpacking libtdb1:amd64 (1.3.8-0ubuntu0.14.04.1) ... Selecting previously unselected package libogg0:amd64. Preparing to unpack .../libogg0_1.3.1-1ubuntu1_amd64.deb ... Unpacking libogg0:amd64 (1.3.1-1ubuntu1) ... Selecting previously unselected package libvorbis0a:amd64. Preparing to unpack .../libvorbis0a_1.3.2-1.3ubuntu1_amd64.deb ... Unpacking libvorbis0a:amd64 (1.3.2-1.3ubuntu1) ... Selecting previously unselected package libvorbisfile3:amd64. Preparing to unpack .../libvorbisfile3_1.3.2-1.3ubuntu1_amd64.deb ... Unpacking libvorbisfile3:amd64 (1.3.2-1.3ubuntu1) ... Selecting previously unselected package libcanberra0:amd64. Preparing to unpack .../libcanberra0_0.30-0ubuntu3_amd64.deb ... Unpacking libcanberra0:amd64 (0.30-0ubuntu3) ... Selecting previously unselected package libxcb-util0:amd64. Preparing to unpack .../libxcb-util0_0.3.8-2ubuntu1_amd64.deb ... Unpacking libxcb-util0:amd64 (0.3.8-2ubuntu1) ... Selecting previously unselected package libstartup-notification0:amd64. Preparing to unpack .../libstartup-notification0_0.12-3ubuntu1_amd64.deb ... Unpacking libstartup-notification0:amd64 (0.12-3ubuntu1) ... Selecting previously unselected package firefox. Preparing to unpack .../firefox_50.0+build2-0ubuntu0.14.04.1_amd64.deb ... Unpacking firefox (50.0+build2-0ubuntu0.14.04.1) ... Selecting previously unselected package xul-ext-ubufox. Preparing to unpack .../xul-ext-ubufox_3.2-0ubuntu0.14.04.1_all.deb ... Unpacking xul-ext-ubufox (3.2-0ubuntu0.14.04.1) ... Processing triggers for mime-support (3.54ubuntu1.1) ... Processing triggers for man-db (2.6.7.1-1ubuntu1) ... Setting up libtdb1:amd64 (1.3.8-0ubuntu0.14.04.1) ... Setting up libogg0:amd64 (1.3.1-1ubuntu1) ... Setting up libvorbis0a:amd64 (1.3.2-1.3ubuntu1) ... Setting up libvorbisfile3:amd64 (1.3.2-1.3ubuntu1) ... Setting up libcanberra0:amd64 (0.30-0ubuntu3) ... Setting up libxcb-util0:amd64 (0.3.8-2ubuntu1) ... Setting up libstartup-notification0:amd64 (0.12-3ubuntu1) ... Setting up firefox (50.0+build2-0ubuntu0.14.04.1) ... update-alternatives: error: alternative path /usr/bin/firefox doesn't exist dpkg: error processing package firefox (--configure): subprocess installed post-installation script returned error exit status 2 Setting up xul-ext-ubufox (3.2-0ubuntu0.14.04.1) ... Processing triggers for libc-bin (2.19-0ubuntu6.9) ... Errors were encountered while processing: firefox E: Sub-process /usr/bin/dpkg returned an error code (1)
那么这个错误到底是什么？我搜索过但无法解决。
apt-cache policy firefox：
firefox:
Installed: 50.0+build2-0ubuntu0.14.04.1
Candidate: 50.0+build2-0ubuntu0.14.04.1
Version table:
*** 50.0+build2-0ubuntu0.14.04.1 0
500 http://ppa.launchpad.net/ubuntu-mozilla-security/ppa/ubuntu/ trusty/main amd64 Packages
100 /var/lib/dpkg/status
50.0~b11+build1-0ubuntu0.14.04.1 0
500 http://ppa.launchpad.net/mozillateam/firefox-next/ubuntu/ trusty/main amd64 Packages
49.0.2+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
28.0+build2-0ubuntu2 0
500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
我如何切换回 Firefox 的稳定发布分支？