Customize toolbars option and menu bar greyed out (i.e. disabled)

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Right-click on a toolbar and select Customize
2. Drag a toolbar button from the new window that just opened onto any Firefox 
toolbar and select Finish
3. Now right-click a toolbar and select Customize again
4. The Customize window won't open and from now on the Customize option (as 
well as the menu bar) will be greyed out, i.e. disabled

What is the expected output? What do you see instead?
The Customize option (and menu bar) should keep working even after you have 
added something to a toolbar.

What version of the product are you using? On what operating system?
Latest Firefox 7 stable (7.0.1.) on both Win XP Pro SP3 and Win 7 Pro x64 SP1, 
latest version of the addon (3.2).

Original issue reported on code.google.com by [email protected] on 9 Oct 2011 at 1:20