I have seen the same thing. Typically I have half a dozen doc tabs open and sometimes I have a calendar tab open but not too often.
What I really hate is when I have 10 tabs open and I have to restart FireFox because it is over 1 GB of virtual memory: I don't want to have to reopen all of the tabs again. So I use Process Explorer to kill off FireFox. When I restart it, FireFox gives me the chance to restore my last session, which I do. FireFox is then back running again with all of the tabs that were there when I killed it and memory usage is down to a fraction of what it was before.
What I really hate is when I have 10 tabs open and I have to restart FireFox because it is over 1 GB of virtual memory: I don't want to have to reopen all of the tabs again. So I use Process Explorer to kill off FireFox. When I restart it, FireFox gives me the chance to restore my last session, which I do. FireFox is then back running again with all of the tabs that were there when I killed it and memory usage is down to a fraction of what it was before.