Fluid supports user scripts which are essentially javascript codes to modify the behavior of the website (also styles to modify its looks).
Once you've created you app, right click on the icon in the status bar, and access the user scripts. Create a new one that will target the appropriate url (in my case Facebook.com) and add the following code. Not getting into too much details, but basically it will count for 60 seconds after the last user interaction with the document, to prevent the page from reloading while we are doing something.
var refreshRate = 600; //<-- In seconds, change to your needs
var lastUserAction = 0;
function resetCounter(){
lastUserAction = 0;
}
setInterval(function(){
lastUserAction++;
if(lastUserAction >= refreshRate){
window.location.reload();
lastUserAction = 0;
}
}, 1000);
document.onkeypress = resetCounter;
document.onmousemove = resetCounter;