Not likely, but worth a blow job (nj). Side panels been off for years, hdd is outside the case and doesn't seem overly hot.

Clean boot and (apparently) shutdown this morning. My suspicion now points to a FF memory leak maxing out the swap file over time, preventing a clean shutdown or (eventually) causing a hard crash. xp appears to be unaffected and has carried on as per usual.

This may help: https://addons.mozilla.org/en-US/firefox/addon/ramback/

Disk issues, or file system issues?

https://en.wikipedia.org/wiki/Fsck

Oh. zombie thread.  :-$