We should be consistent with the id format we're using, and also trying to be more unique. In widget we uses the addon's id to create a more unique id for the element, and in `button` I used a similar approach: however, I was limited by the limitation of the `CustomizableUI`, where only alphanumeric characters, plus hyphen and underscore, could be used. See: https://github.com/mozilla/addon-sdk/pull/1038/files#L3R21