Issue 4248: Breakpoints don't work anymore, if iframe is removed, that shares the JS file with the main page

Steps to reproduce

  1. Open Firebug
  2. Enable and switch to the Script panel
  3. Reload the page
  4. In issue4248.js set a breakpoint at line 3 (if (!document.getElementById("iframe")))
  5. Click the Add iframe button
    ⇒ Script execution is stopped at line 3
  6. Continue script execution by pressing F8
  7. Click the Remove iframe button
  8. Click the Add iframe button again

Observed result

Expected result