• Close Firefox.
• Go to Start > Run
• Type firefox.exe -profilemanager and hit OK
• The profile manager will launch and you should see more than one profile listed - Usually just two. Select the other one.

Usually this is the problem. If your profile isn't listed, you may still be able to recover your bookmarks. Enter the following in the address bar in explorer:

%HOMEDRIVE%%HOMEPATH%\Application Data\Mozilla\Firefox\Profiles

You should see one or more folders with random names. Each one is a profile. Firefox stores bookmarks in these folders as the following:

bookmarks.html - The current bookmarks
bookmarks.bak - Backup from last change to guard against system errors
\bookmarkbackups\ - Daily backups spanning five days