Did you try the code I gave you? It works all right for me in Edge and IE.
It doesn't work in some other browsers, because it's up to each browsers how it displays XML. If you want a particular look, don't depend on that - instead, generate HTML from your XML and include you <br /> elements there. XML is all about data, not the look.
You should also consider changing the structure of your XML. Having an individual element for each message probably makes better sense.
@Jovan: He said that line breaks are correct in the XML file; his problem is only about displaying it in browsers.