if you;re local in IE9, localStorage won't work. you have dom storage behaviors, and that's it. You can however read and write files by renaming the html file to .hta. I actually had an app that saved a json blob inside it's own hta file: to save it would load itself, split the file apart at the json section, sandwich in the new json stringification, and save the hta file over itself. A little different i realize, but it did the job i needed it too.
BROWSER STATS [% share]
(2013/10/31) IE7:0.5, IE8:8.6, IE9:5.3, IE10:12.3, FF:17.7, CH:41.8, SF:8.1, MOBILE:20.4