Issue 4818: frame.eval fails for everthing but the newest frame of the stack

Steps to reproduce

  1. Open Firebug UI, enable the Script panel, reload the page.
  2. Click this button to break on line 20
  3. Create two new watch expressions in the Watch panel: v1 and v2
  4. The Watch panel should show v1: is not defined and v2: "value2"
  5. Click on func1 bread-crumb (Script panel toolbar) to change the current (debug) frame.
  6. The Watch panel should show v1: "value1 and v2: is not defined