gmail and firefox

I use gmail now for my mail, and firefox as my main web browser. One thing that I like about firefox is its ability to have multiple tabs open and save them when I exit it and reopen all my tabs when I open it again so I enter my browsing experience just like I left it. But it is slow on an old computer like mine is (I only have 256 MB of memory which I think is the important factor here) so I try to keep the flags to a minimum (I usually have about 10 open though between sessions). One flag that I always had open was my gmail but not any more after I found this extension to it. Now I have a little gmail notification at the bottom of my browser and a number behind it that tells me how many mails I have unread in my mailbox, pretty nifty.