Charliejay,
Judging from my web searches, This malware, officially called ransomware, has been infecting PC's for many months. It is called ransomware because it wants you "to pay a ransom" to release your computer. It is not the FBI, or any other actual agency, trying to hack your computer. It just makes the particular browser that you were using at the time unusable, until it is ransomed or has the malware removed.
Since it has recently infected several Mac users, I reached a hypothesis that this malware, which has gone through many generations in the PC world, has gone through another modification that makes it able to affect us Mac users.
As far as "silly" things, I was focused on what I was doing, and not so focused on what might have been happening in the background.