If I try running ./interlink -P, it brings up profile information and I can play around with the dialog box right up until it tries to load the "meat" of the program, so I know the executable isn't totally faulty. Playing around with GDB isn't helping much, and it feels like a very similar kind of situation to the NSS issues I was having earlier. All I know is that an attempt to initialize something (or possibly even a FAILURE to attempt to initialize something?) is probably causing everything to blow up, only this time I have even less information. It usually prints nothing relevant to the console even with a debug build and appears to exit normally.
So basically, the program's execution goes like this. The main execution loop in nsMailApp.cpp starts up fine, it loads in libxul.so without much of a problem, and then the last library that gets loaded in before the crash is libpixbufloader-png.so. I don't think that library is the problem, though.
After loading in that library, the program continues spinning up new threads as it goes through XREMain in nsAppRunner.cpp. Everything looks fairly normal until it hits RecordShutdownEndTimeStamp, at which point I think it might be clear something is going wrong, but I don't know what. Then I'm back in nsMailApp watching it go through nsCOMPtr<nsIFile> statements. After nsCOMPtr<nsIFile> appini, suddenly I've hit NS_LogTerm, by which point it's clear the application is definitely shutting down and not starting up. It's weird, because when I compare it with the navigator, nsNavigatorApp.cpp looks just like nsMailApp.cpp, so I don't see why that should be working while this fails.
As far as I can tell, the application is going straight from the startup to the shutdown without doing anything at all in the middle, or if it is doing anything in the middle I don't know where to look for it. So yeah... if anyone was looking forward to this being done quickly just because I got the browser to work somehow (I know I was looking forward to it), it's going to be a while. I estimate this will take me another 2 weeks to a month. I'm not giving up, though!
On a more positive note, here are some screenshots of the progress I've made so far...