According to this article http://wiki.eclipse.org/FAQ_How_do_I_load_and_save_plug-in_preferences%3F we’re supposed to use preferences as shown below.
Preferences prefs = new InstanceScope().getNode(MY_PLUGIN_ID);
How do I put it in a field editor preference page.
Use
ScopedPreferenceStoreand overrideIPreferencePage.doGetPreferenceStore()to make it available for the dialog.