* In February of this year, there was a discussion [1] in which we decided that the minimum supported version of Mac OS X would be 10.5 (Leopard)

* Early in the summer we decided to not yet provide supported 64-bit builds on Windows [2], and will instead work on delivering those in some future release.

* In July we decided that the minimum supported version of Windows would be Windows 2000 [3]

* After some evaluation [4] we decided this week to drop support for OSX/PPC; Firefox 4 Mac OS X binaries will ship as universal builds for i386/x86-64 only

* We are considering dropping support for i386 architectures which do not support SSE2 [5] (older Athlon CPUs, some VIA chipsets) but have not yet reached a final decision here.