Someone asked this question here: https://support.mozilla.org/en-US/questions/1273320 ...And despite getting a really stupid answer, apparently accepted it. I don't WANT to make the pane narrower - obviously. I need to read what's in it. That's why I want the Layout Pane to go UNDER the HTML Pane, so I can get the full width. So... I'll repeat the old, archived question: How can I fix the Inspector Layout Pane to be UNDER the HTML Pane - always - regardless of how wide it is.