diff -uNrBbwp palemoon-29.4.6/palemoon/palemoon/base/content/nsContextMenu.js palemoon-29.4.6-new/palemoon/palemoon/base/content/nsContextMenu.js

--- palemoon-29.4.6/palemoon/palemoon/base/content/nsContextMenu.js	2022-05-07 15:30:02.000000000 +0000

+++ palemoon-29.4.6-new/palemoon/palemoon/base/content/nsContextMenu.js	2022-05-07 19:41:05.288308336 +0000

@@ -198,7 +198,10 @@ nsContextMenu.prototype = {

 #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 = shell.canSetDesktopBackground;

     }

 #endif