--- a/browser/base/content/nsContextMenu.js	
+++ a/browser/base/content/nsContextMenu.js	
@@ -210,13 +210,15 @@ nsContextMenu.prototype = {
     // Set as Desktop background depends on whether an image was clicked on,
     // and only works if we have a shell service.
     var haveSetDesktopBackground = false;
 #ifdef HAVE_SHELL_SERVICE
     // Only enable Set as Desktop Background if we can get the shell service.
     var shell = getShellService();
-    if (shell)
+    var env = Components.classes["@mozilla.org/process/environment;1"]
+                        .getService(Components.interfaces.nsIEnvironment);
+    if (shell && env.get('DESKTOP_SESSION') == "gnome")
       haveSetDesktopBackground = true;
 #endif
     this.showItem("context-setDesktopBackground",
                   haveSetDesktopBackground && this.onLoadedImage);
 
     if (haveSetDesktopBackground && this.onLoadedImage) {