Don't blow up if the user hasn't yet clicked the content when moving around in caret mode.

common/content/editor.js

@@ -424,6 +424,11 @@ const Editor = Module("editor", {
                         count = 1;
 
                     let controller = buffer.selectionController;
+                    let sel = controller.getSelection(controller.SELECTION_NORMAL);
+                    if (!sel.rangeCount) // Hack.
+                        sel.addRange(RangeFind.endpoint(
+                            RangeFind.nodeRange(tabs.localStore.focusedFrame.document.documentElement),
+                            true));
                     while (count--)
                         controller[caretModeMethod](caretModeArg, false);
                 },