Hi, here's a suggestion. I think it would be a good idea to replace the browser's `confirm()` function with a modal window to confirm actions like removing an ad or deleting an account. It would look much more aesthetically pleasing and better integrated with the theme.

Yes, but generally it's theme functionality so layout match to theme.
Osclass used to have these in old themes (I think from some jQuery plugin) but these confirms are not used really often and it was just dropped... usually, browser native functionality is best.