I think I've managed to find the cause of this: winbind!
This was my nsswitch.conf file:
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.
I think I've managed to find the cause of this: winbind!
This was my nsswitch.conf file:
# /etc/nsswitch.conf doc-reference' and `info' packages installed, try:
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-
# `info libc "Name Service Switch"' for information about this file.
passwd: compat winbind
group: compat winbind
shadow: compat
hosts: files wins mdns4_minimal [NOTFOUND=return] dns mdns4
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
I removed all references to winbind from this file and did an 'aptitude remove winbind'
Firefox is now stable, tried re-installing flash and re-activating my plugins, no crashes since!
Someone else with a 64-bit machine should now try to re-create this if possible and then hopefully we will have a definitive way to reproduce this.
Is it a firefox bug or a winbind bug? Should a seperate bug be raised as a winbind issue?