--- a/widget/WidgetEventImpl.cpp
+++ b/widget/WidgetEventImpl.cpp
@@ -558,18 +558,20 @@ WidgetKeyboardEvent::GetShortcutKeyCandi
       ShortcutKeyCandidate key(ch, true);
       aCandidates.AppendElement(key);
     }
   }
 
   // Special case for "Space" key.  With some keyboard layouts, "Space" with
   // or without Shift key causes non-ASCII space.  For such keyboard layouts,
   // we should guarantee that the key press works as an ASCII white space key
-  // press.
-  if (mCodeNameIndex == CODE_NAME_INDEX_Space &&
+  // press.  However, if the space key is assigned to a function key, it
+  // shouldn't work as a space key.
+  if (mKeyNameIndex == KEY_NAME_INDEX_USE_STRING &&
+      mCodeNameIndex == CODE_NAME_INDEX_Space &&
       pseudoCharCode != static_cast<uint32_t>(' ')) {
     ShortcutKeyCandidate spaceKey(static_cast<uint32_t>(' '), false);
     aCandidates.AppendElement(spaceKey);
   }
 }
 
 void
 WidgetKeyboardEvent::GetAccessKeyCandidates(nsTArray<uint32_t>& aCandidates)
@@ -602,18 +604,20 @@ WidgetKeyboardEvent::GetAccessKeyCandida
       if (aCandidates.IndexOf(ch[j]) == aCandidates.NoIndex) {
         aCandidates.AppendElement(ch[j]);
       }
     }
   }
   // Special case for "Space" key.  With some keyboard layouts, "Space" with
   // or without Shift key causes non-ASCII space.  For such keyboard layouts,
   // we should guarantee that the key press works as an ASCII white space key
-  // press.
-  if (mCodeNameIndex == CODE_NAME_INDEX_Space &&
+  // press.  However, if the space key is assigned to a function key, it
+  // shouldn't work as a space key.
+  if (mKeyNameIndex == KEY_NAME_INDEX_USE_STRING &&
+      mCodeNameIndex == CODE_NAME_INDEX_Space &&
       charCode != static_cast<uint32_t>(' ')) {
     aCandidates.AppendElement(static_cast<uint32_t>(' '));
   }
   return;
 }
 
 /* static */ void
 WidgetKeyboardEvent::Shutdown()