I was able to get it to start by:
:/opt/firefox$ sudo ln -s /usr/lib32/libglib-2.0.so.0 libdbus-glib-1.so.2
However, it would only start once. After a close and restart the error message was:
/opt/firefox/firefox-bin: symbol lookup error: /opt/firefox/components/libdbusservice.so: undefined symbol: dbus_connection_setup_with_g_main
If I open up 3.0.12 firefox and then close it firefox 3.5.1 will again start 1 time only but all the plugins show errors:
LoadPlugin: failed to initialize shared library libXt.so [libXt.so: cannot open shared object file: No such file or directory]
LoadPlugin: failed to initialize shared library libXext.so [libXext.so: cannot open shared object file: No such file or directory]
LoadPlugin: failed to initialize shared library /usr/lib/xulrunner-addons/plugins/libnullplugin.so [/usr/lib/xulrunner-addons/plugins/libnullplugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/xulrunner-addons/plugins/libunixprintplugin.so [/usr/lib/xulrunner-addons/plugins/libunixprintplugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-basic-plugin.so [/usr/lib/totem/gstreamer/libtotem-basic-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-complex-plugin.so [/usr/lib/totem/gstreamer/libtotem-complex-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-cone-plugin.so [/usr/lib/totem/gstreamer/libtotem-cone-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-gmp-plugin.so [/usr/lib/totem/gstreamer/libtotem-gmp-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-mully-plugin.so [/usr/lib/totem/gstreamer/libtotem-mully-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-narrowspace-plugin.so [/usr/lib/totem/gstreamer/libtotem-narrowspace-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/jvm/java-6-openjdk/jre/lib/amd64/gcjwebplugin.so [/usr/lib/jvm/java-6-openjdk/jre/lib/amd64/gcjwebplugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-dvx.so [/usr/lib/mozilla/plugins/mplayerplug-in-dvx.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-qt.so [/usr/lib/mozilla/plugins/mplayerplug-in-qt.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-rm.so [/usr/lib/mozilla/plugins/mplayerplug-in-rm.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-wmp.so [/usr/lib/mozilla/plugins/mplayerplug-in-wmp.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in.so [/usr/lib/mozilla/plugins/mplayerplug-in.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/xulrunner-addons/plugins/librhythmbox-itms-detection-plugin.so [/usr/lib/xulrunner-addons/plugins/librhythmbox-itms-detection-plugin.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-dvx.so [/usr/lib/mozilla/plugins/mplayerplug-in-dvx.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-qt.so [/usr/lib/mozilla/plugins/mplayerplug-in-qt.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-rm.so [/usr/lib/mozilla/plugins/mplayerplug-in-rm.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in-wmp.so [/usr/lib/mozilla/plugins/mplayerplug-in-wmp.so: wrong ELF class: ELFCLASS64]
LoadPlugin: failed to initialize shared library /usr/lib/mozilla/plugins/mplayerplug-in.so [/usr/lib/mozilla/plugins/mplayerplug-in.so: wrong ELF class: ELFCLASS64]
/
Seems like it's trying to call 64-bit xulrunner/plugins which doesn't seem to work well on a 32-bit firefox. ](*,)
So I guess the question is "Is this supposed to work on 64-bit ubuntu?".