When a website is hit from two different browsers running on same computer. what are the properties that differ?
The source port for each browser's TCP connection(s) is/are different.
https://www.oreilly.com/library/view/http-the-definitive/1565925092/ch04s01.html
A TCP connection is distinguished by four values:
<source-IP-address, source-port, destination-IP-address, destination-port>
Together, these four values uniquely define a connection. Two different TCP connections are not allowed to have the same values for all four address components