Handle navigation keys when viewer is not focused

Restrict the scrollbar hack to the keycode for "spacebar",
since the bug only occurs in Firefox with spacebar.

Keyboard navigation is only activated for the spacebar if
the currently focused element is not a button.

web/viewer.js

@@ -2160,19 +2160,15 @@ window.addEventListener('keydown', function keydown(evt) {
   // Some shortcuts should not get handled if a control/input element
   // is selected.
   var curElement = document.activeElement || document.querySelector(':focus');
-  if (curElement && (curElement.tagName.toUpperCase() === 'INPUT' ||
-                     curElement.tagName.toUpperCase() === 'TEXTAREA' ||
-                     curElement.tagName.toUpperCase() === 'SELECT')) {
+  var curElementTagName = curElement && curElement.tagName.toUpperCase();
+  if (curElementTagName === 'INPUT' ||
+      curElementTagName === 'TEXTAREA' ||
+      curElementTagName === 'SELECT') {
     // Make sure that the secondary toolbar is closed when Escape is pressed.
     if (evt.keyCode !== 27) { // 'Esc'
       return;
     }
   }
-//#if (FIREFOX || MOZCENTRAL)
-//// Workaround for issue in Firefox, that prevents scroll keys from working
-//// when elements with 'tabindex' are focused.
-//PDFView.container.blur();
-//#endif
 
   if (cmd === 0) { // no control key pressed at all.
     switch (evt.keyCode) {
@@ -2248,6 +2244,29 @@ window.addEventListener('keydown', function keydown(evt) {
         PDFView.rotatePages(90);
         break;
     }
+    if (!handled && !PresentationMode.active) {
+      // 33=Page Up  34=Page Down  35=End    36=Home
+      // 37=Left     38=Up         39=Right  40=Down
+      if (evt.keyCode >= 33 && evt.keyCode <= 40 &&
+          !PDFView.container.contains(curElement)) {
+        // The page container is not focused, but a page navigation key has been
+        // pressed. Change the focus to the viewer container to make sure that
+        // navigation by keyboard works as expected.
+        PDFView.container.focus();
+      }
+      // 32=Spacebar
+      if (evt.keyCode === 32 && curElementTagName !== 'BUTTON') {
+//#if !(FIREFOX || MOZCENTRAL)
+//// Workaround for issue in Firefox, that prevents scroll keys from working
+//// when elements with 'tabindex' are focused. (#3499)
+//      PDFView.container.blur();
+//#else
+        if (!PDFView.container.contains(curElement)) {
+          PDFView.container.focus();
+        }
+//#endif
+      }
+    }
   }
 
   if (cmd === 4) { // shift-key