Just as a heads up, to Windows users using Internet Explorer 9. Discourse will be phasing out support in 2016 for this older browser. This won't mean it stops working immediately, it simply won't be tested as updates are released - if something breaks it will stay broken.
Every version of Windows that runs IE9 is capable of upgrading to at least IE11. I highly recommend the upgrade if you haven't already. Updating your browser makes it faster, lighter, and more compatible - and it's free.
Windows XP doesn't support IE9 or higher, so I recommend Chrome or Firefox for you (or upgrade to Windows 7).
I will update this as the phase out gets closer.
[Not sure which browser you've got? Check here: http://whatbrowser.org]
See also: Phasing Out IE8