Comment 21 for bug 1189989

Pushed to master, along with two follow-ups:

* avoid crashing if an invalid thaw date (e.g., 13/02/2017) is specified (though we really do need to stop kicking that l10n can down the road; I wish Firefox hadn't been so intransigent, and would be open to proposals to add a decent polyfill datepicker for 3.0)
* normalize the capitalization of the onclick attribute

Thanks, Bill, Jason, and Kathy!