I investigated getting Firefox 2 to build with the Mac OS X 10.5 SDK (bug 400165) and it turns out we won’t be completing that work. This does not mean you can’t build Firefox 2 on Mac OS X 10.5, it just means you have to use an SDK for a previous OS release. You will not be able to build Firefox 2 using the 10.5 SDK. There are some nspr/sdk header conflicts that are nasty enough to make it not worth it.
The good news is there aren’t really any good reasons to use the 10.5 SDK. Being too lazy to install SDKs with your developer tools is not a good reason, at least according to me.
If you want to build Firefox 2 on Mac OS X 10.5 you should install the Mac OS X 10.4u SDK and add this line to your mozconfig:
You can also build with the 10.2 and 10.3 SDKs, I’ll leave modifying the above instructions to do that as an exercise for those interested.