[Manchester] Banking Malware and free/open-source software

Hi, was watching this http://www.bbc.co.uk/iplayer/episode/b01c12nz/Click_04_02_2012/ (my dad sent it me )

I was wondering if anyone has any thoughts about this - specifically if, in the "man in the browser" area, the threat level in FreeSoftware is the same as in Proprietary?

I am aware that many FOSS users claim malware is less likely to a) be made for OS's like Debian and b) Will be less effective due to the design of these OS's if it is made - however these financial attacks seem to focus mostly on the browser - does this mean that firefox on windows and firefox on ubuntu are equally vulnerable?

Best

Anna