A lot of apps require information from your screen to work. If you don't have Alt1 installed you can use screenshots to provide the apps with pixel information.
To make a screenshot press the screenshot button on your keyboard, make sure the Runescape window is visible on your screen while you do this. Now make sure you clicked the app in which you want to paste by clicking anywhere in it. After this just press Ctrl+V to paste the screenshot into the app, the app will now process the screenshot automatically. Feel free to post a question in the shoutbox to the bottom left if you have any problems.
Alt1 is an application made by RuneApps to allow webapps to run a lot smoother and outside of your browser. You can give websites permission to see your screen on Alt1, this allows apps to work very smoothly and without the need for the screenshot work-around.
For more info check out the Alt1 page.