That's funny, because the reason I finally broke down and tried a 64-bit build (of 7.0.1) is because the 32-bit build kept crashing repeatedly for me, and I just got sick of it... For a while, I went back to 5, which was the last one that was rock-solid for me, but eventually when I saw Adobe was now officially supporting the 64-bit Flash plugin, I decided to give 64-bit Firefox a try... And, you know what? It's damn near rock-solid again! I think I had maybe 1 crash total with 7.0.1 64-bit in all the time I used it, and so far have had none with 8.0 64-bit... So, I think you guys have things a bit backwards: it's your 32-bit builds that could really use stabilizing and improvement, while your 64-bit builds are far superior!
(I'm on CentOS 5, so the cause is probably some ancient lib version or something... But, all I know is the 64-bit build seems to work great, so I'm sticking with it...)
Still, even if you're not promoting it, I'd think you could detect we were already running a 64-bit version, which means we obviously want to continue doing so, and offer up the new 64-bit version for download instead of the 32-bit one... I'm not saying offer it to someone currently running a 32-bit version... *shrug*