I feel like an idiot but I cannot find it. Meanwhile, if the post is long and has a lot of LaTeX formulae in it, and the connection is imperfect, the wysiwyg regime is a non-stop fight. I figured out I can force the page script to stop manually by clicking the browser stop button but I do not think that was the intended idea. Please, enlighten me as to where the good old "one shot preview" option is now...