firefox shutdown

[#1]

When I finish surfing and close firefox ,it stays running in the background. If i wish to go back in I have to stop the session using Ctrl_,ALt_del select firefox and del.Before I can then
restart it.  Is this a virus ?  AVG scans the drives as free of viruses but ?
                                      WILT

[#2]

I have a similar issue with Outlook sometimes.  It doesn't close properly, and i have to close it manually, before I can reopen it.
I've only recently started to use Firefox, and never encountered the same thing with that.
John