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