Make multiple track selection and copying possible

I made the mistake of trying to select & copy data on two tracks to append to the ends of those same two tracks and my browser locked up. I kept getting a message saying that the browser wasn't responding and telling me to either close the browser and lose the the work, or wait forever, while it stayed locked up, (with no way to know whether or not anything was even happening on the server). I created my first 16 bars yesterday using this program and it took me 15 hours. Uuugh! 

PLEASE create a way to select a large amount of data on one or more tracks, copy and append it to the end of the tracks.