remove switching tabs keybinds

In newer version of firefox of mac, C-right and C-left switch selected tab
twice.
It seems that these keybinds are now firefox default settings (at least
        as for mac) so remove them so that these keybind moves selected
tab only once.
I do not know if this change works also in other platforms like windows and
linux.

_keysnail.js

@@ -1021,10 +1021,10 @@ key.setEditKey('C-o', function (ev) {
     command.openLine(ev);
 }, '行を開く (Open line)');
 
-key.setGlobalKey('C-<right>', function (ev) {
-    getBrowser().mTabContainer.advanceSelectedTab(1, true);
-}, 'ひとつ右のタブへ');
-
-key.setGlobalKey('C-<left>', function (ev) {
-    getBrowser().mTabContainer.advanceSelectedTab(-1, true);
-}, 'ひとつ左のタブへ');
+//key.setGlobalKey('C-<right>', function (ev) {
+//getBrowser().mTabContainer.advanceSelectedTab(1, true);
+//}, 'ひとつ右のタブへ');
+//
+//key.setGlobalKey('C-<left>', function (ev) {
+//getBrowser().mTabContainer.advanceSelectedTab(-1, true);
+//}, 'ひとつ左のタブへ');