Most of these don’t seem to be Firefox-specific- they just contain the term ‘Firefox’ because Firefox is one of many processes the malware attempts to kill one of many names the malware calls itself on P2P networks.
A couple seem to inject themselves into the Firefox process, but not specifically because they also target IE.
JS_FFSNIFF.A does seem to target Firefox, by posing as a legitimate extension:
Mozilla has taken heat from security experts in the past about neglecting to digitally "sign" third-party extensions so that users have some assurance that Mozilla has vetted the developer's work.
http://blog.washingtonpost.com/securityfix/2006/07/passwordstealing_trojan_disgui.html
This story of course was about a Trojan that could install itself as an extension without any user interaction, although it did require the user to run an .exe file. :o
Some of the other malware listed by Secunia seem to be exploits for long-patched vulnerabilities in older versions.
So keeping up to date, not installing extensions from unknown sites and not running executables from email attachments seems to be enough to keep safe even without the extra precautions you mention Polonus.
Still, there’s no denying that Firefox is becoming a target for the malware writers.
