Normally, the Page Setup button in Print Preview (or the Page Setup command on the File menu on the classic menu bar) opens a small dialog window. So that definitely sounds broken.

Two steps here:

(1) To try to fix the bad printer setting, which could be a paper size issue, try the printer reset described in this article: Fix printing problems in Firefox.

If you prefer not to manually edit the prefs.js file, the numerous preferences for each of your printers are listed in about:config and you can right-click > Reset each of them to clear their value.

(2) To try to fix the bad Page Setup dialog, you can rename the settings file that stores information about window and dialog sizes. That file may have become corrupted.

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button. This should launch a new window showing files and folders.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then rename xulstore.json to something like xulstore.old

Start Firefox back up again. Any improvement in the Page Setup dialog?

Separate Issue; Your System Details shows;

Installed Plug-ins

Adobe PDF Plug-In For Firefox and Netscape 11.0.10 Adobe PDF Plug-In For Firefox and Netscape "9.5.5"

Shockwave Flash 16.0 r0

Adobe Shockwave for Director Netscape plug-in, version 12.1.2.152 Adobe Shockwave for Director Netscape plug-in, version 12.0.9.149

Having more than one version of a program may cause issues.

Go to adobe.com and download the current full installers. Then remove the above programs before using the installers.