
The Firestorm Team announced last Friday (2/13) that they will be blocking their viewer version 4.6.1. Versions 4.6.5, 4.6.7 and 4.6.9 will be the only versions that can log into Second Life. They strongly advise that you upgrade to and use version 4.6.9.
Official Firestorm Announcement is here.
An exception is being made for version 4.4.2 on the Mac side. The problems from Apple’s change to Cocoa have been the reason for this version being allowed to stay on the grid. The Linden position is the problems are from Apple’s upgrades and they are fixed in new Apple Operating System (OS) versions. I understand the updates are free, so there is little reason not to upgrade. But, old hardware can be a problem. But, some decent machines are going for US$200 on eBay.