Chrome and Firefox here are an example for "Two users who use exactly the same hardware but different software".

To distinguish between users between of a larger set, you do more such tests and add them all together. Each test adding a few bits of information.

To make the above code more reliable, you can measure the ratio multiple times:

https://jsfiddle.net/dov1zqtL/

I get 9-10 in Firefox and 3-4 in Chrome very reliably when measuring it 10 times.