AB-test site provides different results in chrome and firefox

[badartist]

We have an AB test running for our site and is currently live in production. Below is the expectation -

Select a product
Clicking on Add to Bag
Shows a Modal overlay/Popup on the page to proceed to checkout
Previous experience - On clicking add to bag a mini modal appears on the right corner with the updated bag count to proceed to checkout.

Currently when a test is run with Chrome we are getting the previous experience, whereas in firefox we get the intended experience. We are able to get the correct expectation when we try to manually replicate the issue on Chrome in our desktop. The problem seems to be only on webpagetest.

Below are 2 identical tests run on Chrome and Firefox for reference of the issue -
Firefox - https://www.webpagetest.org/result/20022...5212379fb/
Chrome - https://www.webpagetest.org/result/20022...6c2e73970/