Your public projects, groups, images and anything that can be seen by a visitor (i.e. your clients) will work in all browsers, including Internet Explorer (IE) 7.
Please be aware that the capability to see or add annotations on images isn't available to people using IE7 or IE8. Instead of being 'broken' this functionality is simply hidden for people using those browsers.
Browser support for accounts
All accounts (i.e. when you are logged in) are best viewed using Internet Explorer 10+, Firefox, Chrome or Safari. And whilst there's no official support for IE8 or below, the app will function fine using these browsers.