Step 1:
Using either Chrome or Firefox, both have simple built in Developer Tools,
open the problem page with a computer that can access the site.
These instructions only work on desktop browsers, to capture a HAR file with an
iPad using a Mac please follow instructions found here
Step 2:
In the top right corner open the browser menu
In Chrome: click More Tools > Developer Tools > Network
In Firefox: click Web Developer > Network
OR
Right click anywhere on the screen and select "Inspect" or "Inspect Element"
Click "Network"
Step 3:
Check "Preserve Log" (Chrome) or "Persist Logs" (Firefox)
Refresh the page
Step 4:
Now right click anywhere on the list of events that are popping up below
Click "Save all as HAR with content" (Chrome) or "Save All as HAR" (Firefox)