From what you say it seems you have done everything correctly.
I cannot think of anything else.
I am willing to have a look at your site if you let me login. There must be an error somewhere, and I will probably be able to determine what it is if I have a look.
The problem you describe with Opera sounds like an encoding issue: you could try disabling zlib compression from the frontend settings and see if it fixes that problem. But if the buttons do appear and are not clickable, there should be some JavaScript error that you might have missed. The normal behavior is that you click a button and the tip suggestion (coin selection and tip amount) get entered into the form. Then, the user can click on the “send” button. Are you certain that no JavaScript error occurs exactly at the time when you click on the button?
Let me know if you want me to look at it.
best