If you're using WinXP (maybe Win2k? I can't remember), C:\Documents and Settings\[username]\Application Data\Mozilla\Profiles\[MozillaProfile]\
Under your Mozilla profile folder is another folder with a random string for a name. That folder contains all of your Mozilla bookmarks, emails, settings, etc.
For Firebird, mine is C:\Documents and Settings\James\Application Data\Phoenix\Profiles\default\epgjhywg.slt