Issue 5705: HTML panel is not properly updated if an iframe is refreshed

Steps to reproduce

  1. Open Firebug
  2. Switch to the HTML panel
  3. Right-click into the blue <iframe> and choose Inspect Element with Firebug
  4. Right-click the <iframe> again and choose This Frame > Reload Frame
    ⇒ A new <html> element is created inside the HTML panel instead of replacing the old one.
  5. Open the Firefox Error Console
  6. Hover the old <html> element inside the HTML panel
    ⇒ There will be an error displayed: Error: TypeError: can't access dead object Source File: chrome://firebug/content/html/inspector.js Line: 82
  7. Switch to the Script panel and back to the HTML panel
    ⇒ The side panels are not displayed anymore.

Observed result

Expected result