Hi ranjeet44,
it could also be you saved the xfce session logging out or shutting down your system, so it gets restored automatically.
Check MENU -> Settings -> Settings Manager -> Session and Startup and see if you have the Automatically save session on, or if firefox is checked in Application Autostart tab. You can also display session chooser on startup to see if there actually are some saved sessions.
If you cannot find anything there you can delete your saved sessions:rm -f ~/.cache/sessions/*
Then try to logout and login again...
Bye... let us know.