If you're looking to see adoption rate, what you really want to be comparing isn't absolute numbers of Chrome vs Firefox users, but rather the adoption rate of

If you're looking to see adoption rate, what you really want to be comparing isn't absolute numbers of Chrome vs Firefox users, but rather the adoption rate of your add-on vs your potential users. If Chrome has 10,000 potential users of your add-on, Firefox has 100, and you have 98 Chrome users and 2 Firefox users, then the add-on adoption rates are 0.98% for Chrome and 2% for Firefox. Of course that's just shifting the hard bit, which is figuring out who your potential users are.