I had the previous version of Firefox 3.6 installed. It ran fine except when it tried to update to 3.62 it would hangup during the download and never complete it. I eventually installed 3.63 but occasionally the "older" 3.6 version will open and intermittent say you've updated to 3.6. At other time the 3.63 will open and intermittent say you've upgraded to 3.63. Most of the time when I open firefox the 3.63 opens. I only see one version on my harddrive otherwise I would consider deleting the older version. I'm running a MAC with Snow Leopard == This happened == A few times a week == last month or two