Debugger's onNewScript hook is supposed to give tools a chance to set breakpoints in newly introduced JS code before it is executed. However, historically, new ways of introducing scripts to the system (cloning functions; lazy compilation; off-thread compilation) have often failed to report the new code to Debugger. The usual visible effect is that breakpoints are missed. JSScripts should have a flag that is clear when the script is built; set when the script is reported to Debugger; and checked when the script is executed. Since we only report the root of a tree of scripts to Debugger directly, Debugger should mark all the descendants of the script it receives as having been reported. js::LazyScripts should never exist in compartments being debugged, but the point here is to catch unreported scripts. Hence, LazyScripts should have a flag indicating that their parent was reported; and compiling a LazyScript to yield as JSScript should propagate that flag to the JSScript. I'll have a patch for this shortly. Unfortunately, at the moment this would catch more bugs than we can cope with. I'll mark those as blockers of this bug.