I am guessing it is because you minimise Firefox to the Windows Xp task bar but have ot either locked that or set it to be on top so it may disappear from view.

When the task bar is visible left click any space area on the taskbar the popup will have options including

• lock task bar if you tick that the task bar stays the same size
• properties if you click on that you get other options for customising the task bar
• also see http://en.wikipedia.org/wiki/Taskbar

The taskbar wasn't locked, so I did as you suggested. Time will tell if this fixes the problem. When Firefox disappeared, it was the only program to do so. I always open MS Outlook first, then Firefox, then an accounting program I use. On the occasional times that Firefox disappears, the other taskbar tabs slide left. I know that Firefox is still operating because the radio stream continues. When I click an email link to get Firefox back, the taskbar tab is now to the far right.

Not sure why only firerox should slide off the taskbar, but maybe more of an XP problem than firefox. I use Firefox on XPs and have not noticed a problem