Please provide instructions on how to remove that giant annoying pop-up ad for Responsive Site Designer every time I open your HTML editor. It's especially annoying since I had already purchased that program several years ago

The options for what to see when opening the HTML Editor are to open a new document, open the last document you were working on, or open no document. If you choose the last option, you will see a list with the last files you had open. As far as I can tell, that advert you mention hasn't been seen for the last couple of versions. Maybe you need to get a newer version.