Getting Monitor Browser's Internet Usage?

In the company I work for, employees' internet traffic is monitored, and if you download too much, you get a warning, and later there might be more serious consequences. But they don't tell how many kilobytes are too much, and they also don't tell, how much of your "kilobyte budget" you have spent already. So I want to be able to monitor my own internet activity. However, all the programs I found so far watch the whole traffic going through the network card, which, beside the internet usage, includes LAN and mail server communication, which don't count. So, I'm looking for a free portable program that can monitor specifically my browser's internet usage, i.e. the number of kilobytes sent and received by the browser application. It is imperative that the program should be portable, or at least installable without administrator privileges, because I don't have that.