Probably been posted somewhere else, but in case not i found this handy little gadget on the Firefox add-ons section of the website.
It is about 54Kb and you can tell it to update every so many hours and so from within Firefox you can see your total amount of credits, your total amount of RAC (still don't understand that
) or both.Worth a look.
https://addons.mozilla.org/en-US/firefox/addon/2524