Persistent fieldsets Incorrectly determine if localStorage exists

Got a report from killes that his fieldsets weren't working at all, had him check the log and found: Fehler: TypeError: window.localStorage is null. This is causing the JS engine to crash.

Further discussion turned out that he is using FF 24 on Debian testing. I found the following link which is how we actually should be checking for support for localStorage (because apparently FF handles it differently): http://stackoverflow.com/questions/4706347/javascript-comparing-2-checks...

'localStorage' in window && typeof window.localStorage !== 'undefined' && window['localStorage'] !== null;