For HTML files, current options are open in editor, and open in browser. I would add "open in Viewer", using something like {servr} to simply render HTML files in RStudio, just like when previewing Quarto documents. This is because, currently, the only way to see HTML content in Viewer is re-rendering a document, but once the document is rendered, there is no way to see it in the context of the IDE again, which can be confusing.