Most browsers will display standard HTML 4.01 elements about the same on the screen. however, when you introduce CSS (cascading style sheets), in your case - nav_files/css3menu1/style.css, you;ll need to do some further research on which elements are not displaying correctly and modify/add additional style information so that you can get as much compatibility as possible.
I would recommend that you set up a workstation and install as many browser versions as you would expect to support (IE 7-9, Chrome, Safari, Firefox, and Opera). That takes care of more than 95% of your visitors.
root = tkinter.Tk()
buttons=[i for i in range(10)]
#If specific button is pressed, output "YES"
for num in buttons: