Number in address bar

Has anyone noticed there is a number in brackets next to the word Facebook in the title (the blue bar in your browser)? Does anyone know what it is? I noticed today that the more I used the account the lower the number got? it started at 150 and went to around 9 ish.

What is this? Am I just being dumb?

That's the number of requests/notifications you've not read yet, I think.