The compiler changes we were hoping to take advantage of unfortunately made the browser dreadfully unstable -- it couldn't even open a window. We will not mess around with the compiler again until we must use gcc 4.2.
As mentioned previously, there will be no official Firefox 4.0.2 -- TenFourFox 4.0.2 is the same as Firefox 4.0.1, with security patches I have reviewed and applied while we wait for Firefox 5 to enter the beta channel and I can investigate if I can port it. This is part of our commitment to maintain a secure browser regardless of what actual version of Mozilla/Gecko we are using. There should be no compatibility issues. You can see the security issues applied (please note that some will require security privileges to view) by reading the rough draft of the release notes. On final release, these will be in the maintenance changesets, minus test cases so that we don't leak proof-of-concepts for any bugs that are still sec-locked. The patches in question were already approved for Firefox 5 and we are simply backporting them to Firefox 4.
Firefox 5 goes to beta channel tomorrow and I plan to pull source and do some preliminary work on it in between moving into my new house. For now,