I've submitted a previous related question, but I'll try again. After downloading 4.0, I tried to move the download file to my applications folder, got a message asking if I wanted to replace a version already there, and said yes. Poof--3.6 was gone. Then when I clicked on the download file and got the screen to move Firefox to applications folder, I got the message my system would not support it. I have since deleted the download file from my applications folder, as well as all evidence on my deskbox of the download attempts. Now I am without Firefox. I'd like to get 3.6 back, and/or find out why I can't install 4.0.