On OS-X, used NSWorkspace to launch the browser.

src/GUI/FGCocoaMenuBar.hxx

@@ -62,4 +62,9 @@ private:
   
 };
 
+/**
+ * open a URL using the system's web-browser
+ */
+void cocoaOpenUrl(const std::string& url);
+
 #endif // __MENUBAR_HXX

src/GUI/FGCocoaMenuBar.mm

@@ -297,3 +297,10 @@ void FGCocoaMenuBar::hide()
 {
   // no-op
 }
+
+void cocoaOpenUrl(const std::string& url)
+{
+  CocoaAutoreleasePool pool;
+  NSURL* nsu = [NSURL URLWithString:stdStringToCocoa(url)];
+  [[NSWorkspace sharedWorkspace] openURL:nsu];
+}

src/GUI/gui_funcs.cxx

@@ -60,6 +60,10 @@
 #  include <shellapi.h>
 #endif
 
+#ifdef SG_MAC
+# include "FGCocoaMenuBar.hxx" // for cocoaOpenUrl
+#endif
+
 #include "gui.h"
 
 using std::string;
@@ -182,6 +186,15 @@ bool openBrowser(string address)
         }
     }
 
+#ifdef SG_MAC
+  if (address.find("://")==string::npos) {
+    address = "file://" + address;
+  }
+  
+  cocoaOpenUrl(address);
+  return ok;
+#endif
+  
 #ifndef _WIN32
 
     string command = globals->get_browser();