Image dimensions different in Xara and browser?

[MEB]

I´ve checked your file in Xara Xtreme 5 Pro and everything´s fine. It exports correctly at 960x135 px. Make sure you have 96dpi in Bitmap Size and Resolution section in Bitmap Size tab in JPEG Export Bitmap Options.
Another detail you must pay attention: make sure the position of the rectangle uses round numbers in both size and position. I mean NO decimal numbers.