let's define ecommerce as anything that occurs with a browser
It's already an out of date definition. People buy things with their cell phones, some of which don't involve a browser. Then again, maybe people would classify that as m-commerce instead of e-commerce and should be excluded from the total ofr m-commerce.
I think you need to define it a bit more- does the purchase have to be completed in the browser? Does payment have to be made online?