We recommend you to use prism

Posterita has been designed to fit a screen of 1024X768, and we perform all our test using firefox and prism.We do not currently offer support for internet explorer, chrome, safari.

If you want Posterita to feel like a proper application, we highly recommend you to use prism. It will convert a web application like posterita, and make it like a desktop application. Therefore you can get it running all the time and use the whole screen.