Semplice LinuxにFirefoxをインストールできない

使っていますSun PriceLinuxWindows 7のVMwareで。うまくいきますが、Firefoxをインストールできません。

Semplice Linuxは、Debian Sid（不安定なブランチ）とOpenboxデスクトップに基づいています。

これは私が得たものです。

sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
You are about to add the following PPA to your system:
 daily (or even multiple builds per day) for various mozilla projects and branches.

For questions and bugs with software in this archive, please contact <email address hidden> or visit #ubuntu-mozillateam on freenode.
 More info: https://launchpad.net/~ubuntu-mozilla-daily/+archive/ubuntu/ppa
Press [ENTER] to continue or ctrl-c to cancel adding it

Traceback (most recent call last):
  File "/usr/bin/add-apt-repository", line 167, in <module>
    sp = SoftwareProperties(options=options)
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 105, in __init__
    self.reload_sourceslist()
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 595, in reload_sourceslist
    self.distro.get_sources(self.sourceslist)    
  File "/usr/lib/python3/dist-packages/aptsources/distro.py", line 89, in get_sources
    (self.id, self.codename))
aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for Semplice/heaven

編集する:

答えに示されているソースを追加すると、次のようになります。

W: Failed to fetch http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu/dists/unstable/main/source/Sources  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu/dists/unstable/main/binary-i386/Packages  404  Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.
c@c-semplice:~$ sudo apt-get install firefox
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package firefox is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'firefox' has no installation candidate