Comment 8 for bug 1249912

The same issue here with SBA 2.0.3; tried with autosizer-2.0.0-beta.xpi to no avail.
In both versions, manually launching chrome://autosizer/content/prefs.xul works and the wizard appears.
Here's an excerpt from the console (only the errors):

~~~~~~
07:28:13
Error: document.getElementById("addBtn2Toolbar") is null
Source File: chrome://autosizer/content/prefs.js
Line: 27
~~~~~~
~~~~~~
07:28:16
Error: w is null
Source File: chrome://autosizer/content/wizard.js
Line: 18
~~~~~~
~~~~~~
07:28:16
Error: asw is undefined
Source File: chrome://global/content/bindings/wizard.xml
Line: 413
~~~~~~
~~~~~~
07:28:16
Error: asw is undefined
Source File: chrome://autosizer/content/wizard.xul
Line: 1
~~~~~~