Both the monitors load the page in a real browser(Firefox) to calculate the load time. However, there would be a difference in response time values due to the following reason:
The Web page Speed(Browser)
The response time of this monitor is the sum of the load time of every single component in the webpage.
Web Transaction(Browser)
The response time is calculated as per the formula given below.
Response time = Total transaction time / Number of steps (URLs)
The total transaction time includes the following components:
Page Load time - Total time taken to load the complete page.
Content match - Time taken to check whether the enabled keyword is available or not.
Mouse Over actions - Time taken to view the menu list and click on the next URL (page).