Change what you want from within the Print Preview window when going to print something. Changes there are put into effect immediately and can be seen in Print Preview.

Changes made in File > Page Setup don't happen until after something is actually printed and "hold" for the next time the user prints something, but when you open Page Setup thru the Print Preview window those changes are immediate.

I realize that what Firefox does thru the File menu item for Page Setup is different from other similar applications, but it has been like that since "day one" with Phoenix back in 2002.

The Print Preview has the Exact same page setup window as the page setup window under the File menu. The only other option is PRINT on the preview window, which defeats the purpose of the print preview to resize the paper size before printing. You never answered my question. Please do not regurgitate default answer scripts. The reason for this post is to get actual help, not a robot answer like just about all of your other responses and answers which do not work for the majority of users. Where is the page size settings like in all other browsers, where a normal user can change to legal 8.5 x 14 or tabloid 11 x 17? If it's been this way since day one, I would have to say this is a pretty big oversight. Flash starting working for mozilla's forum finally so I uploaded IE's, Chrome, and Firefox's Page Setup windows. You can clearly see 1 glaring thing missing from Firefox's 2-tab settings.

Sorry, my answer wasn't a "robot answer" as you claim, and I find it rather insulting from someone with no posting history in this support forum and then saying that I "regurgitate default answer scripts".

Sorry that you misunderstood about my answer and didn't at least look at File > Page Setup in Firefox as I mentioned to view the correct place to be looking.

The 1st and 2rd screenshot is from Windows Explorer Printing Page setup as one would see thru Internet Explorer or possible thru Chrome as the 2nd screenshot shows, which isn't the Firefox Page Setup feature or the Print Preview feature that I was referring to in my answer. Firefox has its own Page Setup windows that are independent of what comes from the Windows Operating System.

Please see my screenshots of what I was referring to with Firefox Page Setup and Print Preview. And as I mentioned, it is best to make changes thru the Print Preview window which will show the changes immediately after those changes are made.

In Firefox, the paper size is handled as a printer property. While Firefox records printer properties as it discovers them, it does not expose them in a Firefox dialog.

Instead, in Print, next to the name of the printer you plan to use, you can find the Properties button there:

It would be awfully nice if Firefox had a more integrated print view, but the experience of both of the people replying to your question is that printing has been a low priority for Mozilla over the years.

If you want to more easily specify an alternate paper size on the fly without altering printer properties, you could consider using a PDF add-on such as this one:

https://addons.mozilla.org/firefox/addon/page-to-pdf/

Note that this converter uses Firefox's built-in SaveAsPDF() command, so if Print Preview looks bad, the PDF will look equally bad.