onsyncfrompreference not being called - firefox-addon

Question

I'm writing a Firefox add-on and for the <scale> XUL element, onsyncfrompreference doesn't seem to be called (Firefox 14). Here's my preference:
<preferences>
<preference id="pref-sensitivity" name="bbaddon.sensitivity" type="string"/>
...
</preferences>
and here is the scale:
<scale min="1" max="100" increment="1" preference="pref-sensitivity"
id="bb-sensitivity"
onsynctopreference="Application.console.log('onsynctopreference called')"
onsyncfrompreference="Application.console.log('onsyncfrompreference called')" />
The logs are just for debugging at the moment, onsynctopreference is called no problem as it shows up on the console, but there's no entry from onsyncfrompreference. I have a default value defined in defaults.js.

Answer 1

If you look at the implementation of this feature in preferences.xml, onsyncfrompreference will only be called for "editable" elements. As to what is considered "editable", you can see that below. Some elements are always considered editable, others have to specify preference-editable="true" attribute explicitly. In your case it's the latter meaning that your fix would look like this:
<scale min="1" max="100" increment="1" preference="pref-sensitivity"
preference-editable="true" id="bb-sensitivity"
onsynctopreference="Application.console.log('onsynctopreference called')"
onsyncfrompreference="Application.console.log('onsyncfrompreference called')" />

Answer 2

I've worked around this using Javascript:
<script type="text/javascript">
var loaded = false;
//load preferences
var prefs = Components.classes["#mozilla.org/preferences-service;1"]
.getService(Components.interfaces.nsIPrefService)
.getBranch("extensions.bb");
prefs.QueryInterface(Components.interfaces.nsIPrefBranch2);
function loadpref() //call this in the prefwindow onload
{
document.getElementById('bb-sensitivity').value = prefs.getCharPref('sensitivity');
loaded = true;
}
function setpref(sensitivity)
{
if(loaded) //onchange for scale fires before onload for the window
{
prefs.setCharPref('sensitivity',sensitivity);
}
}
</script>
and the scale element:
<scale min="1" max="100" increment="1"
preference="pref-sensitivity"
id="bb-sensitivity"
onchange="setpref(this.value);"
/>
I'll leave this question open for now to see if anyone else can help. I'd still like to do this the 'correct' way.