Quix,
As far as your questions go, i have not installed Firefox 2.0 as of yet. i will wait for the YaST2 Online Update to install it, probably in early November (i run SuSE Linux 9.2 Professional).
What i would recommend is that you check out the known security issues in Firefox 1.5.0.7 (the last stable release), and assess your risks from there. It is known that some security issues were patched in Firefox 2.0. At present though, i have not read any documentation on that issue.
i'm a bit curious that you would consider risks in light of the known security risks of the most popular alternative (Internet Explorer).
Sorry that i could not be of more help. If i find any information, i will forward it to you.
The Kaspersky Anti-Virus is supposed to be pretty good. As far as i am aware, Firefox has always 'played nice' with any anti-virus or anti-spyware software on the market. i've used System Mechanic on Windows machines, and have never had a problem with any iteration of the Firefox browser. Never had a virus get though, aside from one of the first boot sector virii that ever existed...got that from an old floppy i had laying around. It was cured with a simple DOS command.
However as added protection, you may wish to add SPYWARE BLASTER, a freeware application that prevents malware from installing in both Internet Explorer and Firefox. There are no checks to run. Merely update the definitions and enable protection for all unprotected applications. It also blocks tracking cookies in Internet Explorer.