Everything goes black instantly and then BIOS info show up as it reboot.
Actually, I saw something similar (it just went black, no reboot until I did CAD twice), once, when I downloaded a nightly version of what got released in firefox-24.8.1.en-US.os2.zip. At the time, I didn't relate it to FF, because FF had been closed for about 20 minutes. Later, I was wondering if FF had something to so with it because that was the only thing that had changed for a few days. After I rebooted, the "official" release was available before I tried it again, so I got rid of the nightly, and have been using 24.8.1 (how can you tell if it is Beta2?) since then (a few days), with no trouble like that (yet). I have had a couple of cases where other programs (Open Office) would not start, until I closed FF.
I have not seen the high usage problem. I do use SNAP with a quad core AMD Phenom processor, and I have used FLASH a couple of times. VIRTUALADDRESSLIMIT is set to 1536. I also have AdBlock and FLASHBLOCK installed. FLASHBLOCK may be the answer, because it prevents trying to run a lot of FLASH content concurrently.
I am also using the QSINIT loader, which may be setting the video properly, before eCS gets booted. I also use the QSINIT RAM disk, which makes use of the memory above what eCS can normally use, and I use "SET SHELLHANDLESINC=40", which may make some difference (20 is default).