That went well.

Code:
root@0[apt]# dpkg -l mozilla-fire\*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name                Version             Description
+++-===================-===================-======================================================
ii  mozilla-firefox     1.0.4-2             lightweight web browser based on Mozilla
un  mozilla-firefox-gno <none>              (no description available)
ii  mozilla-firefox-loc 1.0.2lang20050405-1 dummy package for transition to mozilla-firefox-locale
ii  mozilla-firefox-loc 1.0.4lang20050515-1 Mozilla Firefox German language/region package

root@0[apt]# apt-get -s install mozilla-firefox
Reading Package Lists... Done
Building Dependency Tree... Done
mozilla-firefox is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 387 not upgraded.

root@0[apt]# apt-get install mozilla-firefox -t unstable
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
  gcc-4.0-base libatk1.0-0 libatk1.0-dev libgcc1 libstdc++6 libxinerama1
Suggested packages:
  mozilla-firefox-gnome-support xprint
Recommended packages:
  libatk1.0-data
The following NEW packages will be installed:
  gcc-4.0-base libxinerama1
The following packages will be upgraded:
  libatk1.0-0 libatk1.0-dev libgcc1 libstdc++6 mozilla-firefox
5 upgraded, 2 newly installed, 0 to remove and 815 not upgraded.
Need to get 8577kB of archives.
After unpacking 2789kB disk space will be freed.
Do you want to continue? [Y/n] y
Get:1 http://ftp.de.debian.org testing/main libgcc1 1:4.0.1-2 [89.4kB]
Get:2 http://ftp.de.debian.org testing/main gcc-4.0-base 4.0.1-2 [174kB]
Get:3 http://ftp.de.debian.org testing/main libatk1.0-dev 1.10.1-2 [94.2kB]
Get:4 http://ftp.de.debian.org testing/main libatk1.0-0 1.10.1-2 [68.5kB]
Get:5 http://ftp.de.debian.org testing/main libstdc++6 4.0.1-2 [353kB]
Get:6 http://ftp.de.debian.org unstable/main libxinerama1 6.8.2.dfsg.1-4 [179kB]
Get:7 http://ftp.de.debian.org unstable/main mozilla-firefox 1.0.6-1 [7619kB]
Fetched 8577kB in 19s (446kB/s)
(Reading database ... 359384 files and directories currently installed.)
Preparing to replace libgcc1 1:3.4.3-13 (using .../libgcc1_1%3a4.0.1-2_i386.deb) ...
Unpacking replacement libgcc1 ...
Setting up libgcc1 (4.0.1-2) ...

Selecting previously deselected package gcc-4.0-base.
(Reading database ... 359384 files and directories currently installed.)
Unpacking gcc-4.0-base (from .../gcc-4.0-base_4.0.1-2_i386.deb) ...
Preparing to replace libatk1.0-dev 1.8.0-4 (using .../libatk1.0-dev_1.10.1-2_i386.deb) ...
Unpacking replacement libatk1.0-dev ...
Preparing to replace libatk1.0-0 1.8.0-4 (using .../libatk1.0-0_1.10.1-2_i386.deb) ...
Unpacking replacement libatk1.0-0 ...
Preparing to replace libstdc++6 3.4.3-13 (using .../libstdc++6_4.0.1-2_i386.deb) ...
Unpacking replacement libstdc++6 ...
Selecting previously deselected package libxinerama1.
Unpacking libxinerama1 (from .../libxinerama1_6.8.2.dfsg.1-4_i386.deb) ...
Preparing to replace mozilla-firefox 1.0.4-2 (using .../mozilla-firefox_1.0.6-1_i386.deb) ...
Unpacking replacement mozilla-firefox ...
Setting up gcc-4.0-base (4.0.1-2) ...
Setting up libatk1.0-0 (1.10.1-2) ...

Setting up libatk1.0-dev (1.10.1-2) ...
Setting up libstdc++6 (4.0.1-2) ...

Setting up libxinerama1 (6.8.2.dfsg.1-4) ...

Setting up mozilla-firefox (1.0.6-1) ...
Updating mozilla-firefox chrome registry...done.
Please restart any running Firefoxes, or you will experience problems.

root@0[apt]# dpkg -l mozilla-fire\*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name                Version             Description
+++-===================-===================-======================================================
ii  mozilla-firefox     1.0.6-1             lightweight web browser based on Mozilla
un  mozilla-firefox-gno <none>              (no description available)
ii  mozilla-firefox-loc 1.0.2lang20050405-1 dummy package for transition to mozilla-firefox-locale
ii  mozilla-firefox-loc 1.0.4lang20050515-1 Mozilla Firefox German language/region package
This time, nothing crashed.