I've been using Twenty Thirteen on my blog for some time, but recently realised that the 'Menu' button doesn't seem to be working. When the browser width reaches below a certain width, the theme collapses the menu bar into a single 'Menu' button, which upon clicking should display all the items below.
However, the collapsible 'Menu' button doesn't seem to be working on my website now. Nothing happens when I click it. I do run a copy of Twenty Thirteen and it seems to work fine.
Does anybody have any idea what has happened? Could it be due to caching plugins or other plugins that may affect the 'Menu' button?