Sorry, no, there's no built-in feature for this. And it could be helpful because sometimes Firefox is a little unpredictable when printing selections: it may keep the selection in its relative location on the page rather than moving it to top left. From the paper saving perspective, you could print to PDF to see what you're going to get, and print the PDF to paper if it's satisfactory, but that does involve extra steps. Here are a couple add-ons that allow you to isolate the text you want to print in a way that usually works around most selection printing problems: (1) Print Edit - https://addons.mozilla.org/firefox/addon/print-edit/ With this extension, you call up Print Preview and then make your selection there before printing. (2) Nuke Anything enhanced - https://addons.mozilla.org/firefox/addon/nuke-anything-enhanced/ With this extension, you select in the page normally, right-click, and choose Remove Everything Else. Then you can print normally (i.e., don't choose Selection in the Print dialog). Screen shots in this old post: https://support.mozilla.org/questions/923294?page=2#answer-328405 To view the whole page again, you might be able to right-click Undo remove, or you need to reload the page. (3) Other... I haven't searched for new solutions for a while, so there may well be some new ideas out there.

Using NUKE ANYTHING ADVANCED looks like it will solve the problem. Thanks.