Make sure you include it in build.properties. I would suggest you to create a fragment for the SWT like how SWT does it for each platform. You need to set System property org.eclipse.swt.browser.XULRunnerPath
to the dll. Please refer to
org.eclipse.swt.browser.Mozilla
static void LoadLibraries () {---}
Fragment: http://wiki.eclipse.org/FAQ_What_is_a_plug-in_fragment%3F