For instance: I open whatsapp.com as a web app in a site specific browser instance using firefox --ssb https://web.whatsapp.com Firefox works well for this. However, if I receive a Whatsapp message with a pdf attachment and I click on it, firefox only says the attachment has been downloaded but does not say where and I cannot find the file in any obvious location. Without --ssb, in the same whatsapp web app clicking on an attachment triggers firefox to show a window saying whether to open the file with an application or download it and in the latter case, FF either downloads to the default download location or asks me where to download (depending on my settings).