I discussed with Ayman (our UX guy), and the text should be something like:

"New message from <contact>, <a>read it</a>"

The text between <a></a> is not necessary a link, it could be a <span>, but it should be styled like a link (blue with underlines), so that the user wants to tap it. (but we'll still handle a click event on the entire banner of course)

To replace <contact> in the text, you'll need to use a parameterized l10n value, and use `navigator.mozL10n.localize` to replace it when you show the banner.

For Ayman it's ok if the banner is 2 lines (because sometimes contact names are big) but not more. Maybe Victoria won't agree, we'll see ;)

I'll needinfo someone on the bug to get the final strings but you can start to work from this assumption. Also, when you'll have finished this, I'll ask needinfo on Victoria (our Visual Design woman) to see if that looks ok for her.