859982 - the constructor for preference element behaves differently in-content than in windowed mode

Status: NEW

(Firefox :: Settings UI, defect)

Description

[Christian Sonne [:cers]]

in toolkit/content/widgets/preferences.xml, the constructor for preference elements ends up calling the method updateElements which in turn does:

var elements = document.getElementsByAttribute("preference", this.id);
for (var i = 0; i < elements.length; ++i)
  this.setElementValue(elements[i]);

In the windowed version, the first time this is run, elements.length == 0, so setElementValue isn't called. In the in-content version it isn't, so we call setElementValue which calls the function described in onsyncfrompreference. For the Privacy->Tracking preference(s), this function assumes that the relevant preference elements already have their bindings attached, but that is not guaranteed (it depends on the order in which the preferences privacy.donottrackheader.enabled and privacy.donottrackheader.value are constructed)

If they construct in the wrong order, this causes bug 857236 and possibly other problems nobody has noticed yet.