Add a check if the URL bar selection is fired from user-input.

This overrides the spec for input elements to special-case where we're not actually having the user select anything, but where it results from automatically-generated selections (e.g. autofill).
This should fix #852, but will require Linux testing since Windows doesn't use a primary this way.

browser/base/content/urlbarBindings.xml

@@ -741,6 +741,13 @@
                .getService(Ci.nsIClipboard)
                .supportsSelectionClipboard())
           return;
+        
+        // Check if this selection was actually user-generated, and exit if not
+        // to prevent copying the selection (e.g autofill) to clipboard/primary
+        if (!window.QueryInterface(Ci.nsIInterfaceRequestor)
+                   .getInterface(Ci.nsIDOMWindowUtils)
+                   .isHandlingUserInput)
+          return;
 
         var val = this._getSelectedValueForClipboard();
         if (!val)