Unfortunately, this is a bug in Firefox as it decodes location.hash an extra time when it is accessed. For example, try this in Firefox:
location.hash = "#%30";
location.hash === "#0"; // This is wrong, it should be "#%30"
The only cross-browser solution is to just use (location.href.split("#")[1] || "") instead for getting the hash. Setting the hash using location.hash seems to work correctly for all browsers that support location.hash though.