Over on our community site, BadwareBusters.org, user DrHenley reports ill effects from visiting a badware site using Firefox on Ubuntu:
I could not close FireFox, and it required a reboot to stop the popups. After rebooting the first time I ran FireFox a tab called “My Computer???” came up with the bogus antivirus supposedly scanning the C:\Windows\System folder…(in Ubuntu – ROFL), but I was able to close the tab that time, and it didn’t come back after that.
While there's no evidence that badware penetrated beyond the browser into the OS, this user's experience does show that the browser can be a point of vulnerability, even on Linux.