I am studying the tutorial at https://developer.chrome.com/docs/devtools/javascript/

In "Step 7: Apply a fix", it said "Press Command+S (Mac) or Control+S (Windows, Linux) to save your change."

I save the change, and see there is a warning mark in the tab of the file, saying the "changes to the file is not saved to file system". I ignore that warning. But now when I try to click line number 31 to make a breakpoint, it does not work. There will be no blue mark appear indicating the breakpoint. Why?