I should have mentioned that my previous system (same ISP) ran Ubuntu 7.10 and
an earlier edition of Firefox and that I can leave my PC unattended for up to
four hours before the ISP cuts me off.
Under 7.10 If I left the box alone for long the operating system simply went
into screensaver or powered off the monitor. I never lost Firefox web pages nor
did Firefox ever go into offline mode.
Under 10.04 my internet connection is not severed if I leave it alone for say 40
minutes. The operating system logs me off I must sign in again and Firefox will
have gone into offline mode and lost whatever web pages I had open.