closes #1688, Preferences window appears in wrong screen position on Windows

chrome/content/zotero/overlay.js

@@ -2397,7 +2397,7 @@ var ZoteroPane = new function()
 		};
 		window.openDialog('chrome://zotero/content/preferences/preferences.xul',
 			'zotero-prefs',
-			'chrome,titlebar,toolbar,'
+			'chrome,titlebar,toolbar,centerscreen,'
 				+ Zotero.Prefs.get('browser.preferences.instantApply', true) ? 'dialog=no' : 'modal',
 			io
 		);

chrome/content/zotero/preferences/preferences.xul

@@ -40,7 +40,7 @@ To add a new preference:
 		in Zotero.Prefs.observe()
 
 -->
-<prefwindow id="zotero-prefs" title="&zotero.preferences.title;" onload="moveToAlertPosition(); init()" onunload="Zotero_Preferences.onUnload()"
+<prefwindow id="zotero-prefs" title="&zotero.preferences.title;" onload="init()" onunload="Zotero_Preferences.onUnload()"
 		windowtype="zotero:pref" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
 		style="min-height: 600px">
 	
@@ -840,4 +840,4 @@ To add a new preference:
 	]]>
 	</script>
 	<script src="preferences.js"/>
-</prefwindow>
+</prefwindow>