There have been no changes since the previous Burning Edge post (2004-11-07 branch builds). Firefox 1.0 is the same file as that build, at least for the Windows English zip build (I checked using md5sum).
In keeping with our emphasis on the end-user, we have redesigned the Firefox startpage. We wanted a startpage that reflected the Mozilla project and provided a good access point to the web. Given the importance of search, we decided to add search functionality to the start page itself. Google has long been recognized as a leader in search experience and so we chose Google.