如何解决此问题？

我使用的是PureOS，基本上是Debian，有一些细微的调整。我尝试在上面安装firefox，但结果一团糟。如果现在尝试进行基本升级，则会得到以下信息：

$ sudo apt update && sudo apt upgrade
Ign:1 http://deb.debian.org/debian stretch InRelease
Get:2 http://deb.debian.org/debian stretch-updates InRelease [91.0 kB]              
Get:3 http://deb.opera.com/opera stable InRelease [2592 B]                          
Get:4 http://security.debian.org stretch/updates InRelease [63.0 kB]                
Hit:5 http://deb.debian.org/debian stretch Release                                  
Get:6 https://repo.skype.com/deb stable InRelease [4486 B]                          
Get:7 http://deb.opera.com/opera stable/non-free amd64 Packages [1835 B]            
Get:8 http://packages.microsoft.com/repos/vscode stable InRelease [2801 B]          
Get:9 http://repository.spotify.com stable InRelease [3302 B]                       
Get:10 http://repo.puri.sm/pureos green InRelease [9427 B]                          
Get:12 http://security.debian.org stretch/updates/main Sources [110 kB]             
Get:13 http://security.debian.org stretch/updates/contrib Sources [1384 B]          
Get:14 http://security.debian.org stretch/updates/main amd64 Packages [271 kB]      
Get:15 https://repo.skype.com/deb stable/main amd64 Packages [2251 B]               
Get:16 http://security.debian.org stretch/updates/main Translation-en [120 kB]      
Get:17 http://security.debian.org stretch/updates/contrib amd64 Packages [1776 B]   
Get:18 http://security.debian.org stretch/updates/contrib Translation-en [1759 B]   
Get:19 https://download.sublimetext.com apt/stable/ InRelease [2562 B]              
Get:20 http://packages.microsoft.com/repos/vscode stable/main amd64 Packages [39.6 kB]
Ign:21 https://mega.nz/linux/MEGAsync/Debian_9.0 ./ InRelease                       
Get:22 http://repo.puri.sm/pureos green/main amd64 Packages [6286 kB]               
Get:23 https://mega.nz/linux/MEGAsync/Debian_9.0 ./ Release [976 B]                 
Get:26 http://repo.puri.sm/pureos green/main Translation-en [5583 kB]               
Hit:24 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease      
Get:27 http://repo.puri.sm/pureos green/main amd64 DEP-11 Metadata [2202 kB]        
Get:28 http://repo.puri.sm/pureos green/main DEP-11 64x64 Icons [6768 kB]
Fetched 21.6 MB in 4s (5487 kB/s)                                     
Reading package lists... Done
Building dependency tree       
Reading state information... Done
59 packages can be upgraded. Run 'apt list --upgradable' to see them.
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 iceweasel : Depends: firefox-esr but it is not installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

所以我试图建议：

$ sudo apt --fix-broken install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Correcting dependencies... Done
The following additional packages will be installed:
  firefox-esr
Suggested packages:
  fonts-stix | otf-stix fonts-lmodern mozplugger
The following NEW packages will be installed:
  firefox-esr
0 upgraded, 1 newly installed, 0 to remove and 59 not upgraded.
2 not fully installed or removed.
Need to get 0 B/46.5 MB of archives.
After this operation, 114 MB of additional disk space will be used.
Do you want to continue? [Y/n] 
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = "en_US",
    LC_ALL = (unset),
    LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
(Reading database ... 227765 files and directories currently installed.)
Preparing to unpack .../firefox-esr_52.6.0esr-1~deb9u1_amd64.deb ...
dpkg-divert: error: 'diversion of /usr/bin/firefox to /usr/bin/firefox.real by firefox-esr' clashes with 'diversion of /usr/bin/firefox to /usr/bin/firefox.real by purebrowser'
dpkg: error processing archive /var/cache/apt/archives/firefox-esr_52.6.0esr-1~deb9u1_amd64.deb (--unpack):
 new firefox-esr package pre-installation script subprocess returned error exit status 2
Errors were encountered while processing:
 /var/cache/apt/archives/firefox-esr_52.6.0esr-1~deb9u1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

现在我有点卡住了。

有人知道我能做些什么来清理这个烂摊子吗？欢迎所有提示！

[编辑]

我已尝试通过多种方式删除Firefox：

$ sudo apt -y remove firefox
[sudo] password for hielke: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package 'firefox' is not installed, so not removed
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 iceweasel : Depends: firefox-esr but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

我还尝试了以下变体，但均给出了相似的结果：

sudo apt remove firefox
sudo apt purge firefox
sudo apt remove firefox-esr
sudo apt purge firefox-esr
sudo apt remove iceweasel
sudo apt purge iceweasel
sudo apt remove purebrowser
sudo apt purge purebrowser

[编辑2]

按照@alan的回答，我尝试删除了转移：

$ sudo dpkg-divert --remove /usr/bin/firefox
Removing 'diversion of /usr/bin/firefox to /usr/bin/firefox.real by purebrowser'

之后，我先进行了更新，然后进行了升级：

$ sudo apt update
Hit:1 http://security.debian.org stretch/updates InRelease
Hit:2 http://repo.puri.sm/pureos green InRelease                                                                                         
Hit:3 http://deb.opera.com/opera stable InRelease                                                                                        
Ign:4 http://deb.debian.org/debian stretch InRelease                                                                                     
Hit:5 http://packages.microsoft.com/repos/vscode stable InRelease                                                                        
Hit:6 http://deb.debian.org/debian stretch-updates InRelease                                                                             
Hit:7 http://deb.debian.org/debian stretch Release                                                                                       
Hit:8 https://repo.skype.com/deb stable InRelease                                                                                        
Ign:9 https://mega.nz/linux/MEGAsync/Debian_9.0 ./ InRelease                                                                             
Hit:10 http://repository.spotify.com stable InRelease                                                                                    
Hit:11 https://download.sublimetext.com apt/stable/ InRelease                                                                            
Get:12 https://mega.nz/linux/MEGAsync/Debian_9.0 ./ Release [976 B]                                                                     
Hit:14 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease                          
Fetched 976 B in 3s (385 B/s)                                                                   
Reading package lists... Done
Building dependency tree       
Reading state information... Done
135 packages can be upgraded. Run 'apt list --upgradable' to see     them.
$
$
$
$ sudo apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 iceweasel : Depends: firefox-esr but it is not installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

不幸的是，您看到的结果相同。我apt --fix-broken install只是想确定一下，但是结果和以前一样。

因此，我使用命令查找其他转移（尽管我不确定100％确切地知道哪些转移）：

& sudo dpkg-divert --list | grep firefox
diversion of /usr/share/applications/firefox-esr.desktop to /usr/share/applications/firefox-esr.desktop.diverted by xul-ext-iceweasel-branding

所以我只填写了我认为正确的内容：

$ sudo dpkg-divert --remove /usr/share/applications/firefox-esr.desktop
Removing 'diversion of /usr/share/applications/firefox-esr.desktop to /usr/share/applications/firefox-esr.desktop.diverted by xul-ext-iceweasel-branding'

但我再次得到相同的：

$ sudo apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 iceweasel : Depends: firefox-esr but it is not installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

并尝试修复它：

$ sudo apt --fix-broken install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Correcting dependencies... Done
The following additional packages will be installed:
  firefox-esr
Suggested packages:
  fonts-stix | otf-stix fonts-lmodern mozplugger
The following NEW packages will be installed:
  firefox-esr
0 upgraded, 1 newly installed, 0 to remove and 135 not upgraded.
2 not fully installed or removed.
Need to get 0 B/46.5 MB of archives.
After this operation, 114 MB of additional disk space will be used.
Do you want to continue? [Y/n] 
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = "en_US",
    LC_ALL = (unset),
    LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
(Reading database ... 227763 files and directories currently installed.)
Preparing to unpack .../firefox-esr_52.6.0esr-1~deb9u1_amd64.deb ...
Adding 'diversion of /usr/bin/firefox to /usr/bin/firefox.real by firefox-esr'
Unpacking firefox-esr (52.6.0esr-1~deb9u1) ...
dpkg: error processing archive /var/cache/apt/archives/firefox-esr_52.6.0esr-1~deb9u1_amd64.deb (--unpack):
 trying to overwrite '/usr/share/applications/firefox-esr.desktop', which is also in package xul-ext-iceweasel-branding 0.4.0
dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
Errors were encountered while processing:
 /var/cache/apt/archives/firefox-esr_52.6.0esr-1~deb9u1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

还有其他提示吗？

[编辑3]

按照@harrymc的提示，我尝试运行此命令：

$ sudo apt-get install iceweasel
[sudo] password for hielke: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
iceweasel is already the newest version (52.6.0esr-1~deb9u1).
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 iceweasel : Depends: firefox-esr but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

如您所见，这并没有解决问题。所以这是输出apt-cache policy firefox-esr：

$ apt-cache policy firefox-esr
firefox-esr:
  Installed: (none)
  Candidate: 52.6.0esr-1~deb9u1
  Version table:
     52.6.0esr-1~deb9u1 500
        500 http://security.debian.org stretch/updates/main amd64 Packages
     52.5.0esr-1~deb9u1 500
        500 http://deb.debian.org/debian stretch/main amd64 Packages

仅供参考，以下是我的内容/etc/apt/sources.list：

deb http://repo.puri.sm/pureos/ green main
deb http://deb.opera.com/opera/ stable non-free
# deb-src http://deb.opera.com/opera/ stable non-free
# deb http://security.debian.org/debian-security stretch/updates main
# deb http://httpredir.debian.org/debian/ stretch main contrib non-free

deb http://deb.debian.org/debian stretch main contrib non-free
deb-src http://deb.debian.org/debian stretch main contrib non-free

deb http://deb.debian.org/debian stretch-updates main contrib non-free
deb-src http://deb.debian.org/debian stretch-updates main contrib non-free

deb http://security.debian.org/ stretch/updates main contrib non-free
deb-src http://security.debian.org/ stretch/updates main contrib non-free

这能告诉你什么吗？