`l10n_date.js` might be used by third-party app developers to create localized cross-browser webapps.  For instance, it is mentioned on https://developer.mozilla.org/en-US/Apps/Build/Localization/Localizing_Firefox_OS_Apps#l10n_date_Script.  As much as I like them and find them useful, I'd prefer to avoid using non-ES5 methods like `Math.sign`.

Maybe re-write this code like this?

```
if (Math.abs(secDiff) > 60) {
  secDiff = secDiff > 0 ? Math.ceil(secDiff) : Math.floor(secDiff);
}
```