Fix Bug 1101261 - Visiting www.mozilla.org/firefox/new/ (and others) with an es browser leads to /es-AR/ page.

`CANONICAL_LOCALES` in funfactory could be empty or only `{'en': 'en-US'}`, then Bedrock could override the settings with `{'es': 'es-ES', 'en': 'en-US', 'pt': 'pt-BR'}`.