I'm having the same problem described above.
I reinstalled using the following steps:
1. as root, # killall -9 firefox-bin (it might take a few seconds for firefox-bin to disappear from System Monitor but killall works!)
2. use synaptic to uninstall completely (equivalent to # apt-get purge firefox).
3. in my home directory, rm -rf ./mozilla to completely remove preferences files, etc.
4. then I reinstalled firefox using synaptic.
Result: when I launch Firefox from the menu firefox.bin appears in the System Monitor but no browser window is opened for me.
My workaround was to install the Chromium browser (not Chrome).
It will be interesting to watch and explore this issue to see what is causing this. BTW I have not installed any of the Firefox tools like XMarks or NoScript so Firefox is, at this point, simple and as shipped from the factory.