Hello, I recently fixed http://bugzilla.mozilla.org/show_bug.cgi?id=134066 This allows nsIPromptService dialogs to have accesskeys for checkboxes and buttons, when a label has a character with "&" before it. For example, use the text "Save it &Now" if you want an underlined N, where the user can type Alt+N to activate that button.
If you need a true ampersand, you now must use "&&". - Aaron
