trusted-application

I just lost 5 hours looking for a answer which i haven't been able to find :p First, I'd like to force a trusted application (i need to access the file system) to display into the browser. Based on what i found on google a trusted application must be installed and launched as a desktop application (also called out-of-browser application). So, i want to have an installed application on the client side but meanwhile, the user must also be able to start this same application into a browser window when he goes on my web site. Is this possible ? Second, I'd like to give to the user the possibility