You probably created a new Firefox profile, or switched between profiles without realising it.
This sometimes happens if you open several instances of Firefox at the same time after it crashes.

Try this to fix it:
  • Click Start > Run
  • Run "firefox -profilemanager" from the dialog
  • Select the appropriate profile from the popup


If there is no popup with several profiles to choose from, you only have one, and it really has lost them.
If there is a popup and you don't know which one is the right profile, repeat the list with a different one until they come back.