Where did Page Setup / Margins & Header/Footer go?

New option for users of Firefox 97 and higher: Restoring the Page Setup dialog to the file menu. See https://support.mozilla.org/en-US/questions/1373471#answer-1523526

I'll give you two options with the details to follow:

(1) Become comfortable with entering header/footer detail in the Advanced Configuration Editor (about:config) screen.

(2) Roll back to the old school Firefox approach of separate Print/Preview/Page Setup displays. (I don't know how long this option will be available.)

Left, Center, and Right Header and Footer Preferences

Headers and Footers are split into three parts each of which can contain free-form text and placeholders that Firefox replaces with values computed at print time. The placeholders are:

Here is how you can update your header and footer content for particular printers or all printers:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

Headers

(2) In the search box in the page, type or paste print_h and pause while the list is filtered -- you'll see something like the first screenshot (the exact number of custom preferences depends on how many different printers you have used)

The following three preferences are the default, but any printer-specific value overrides them, allowing you to customize individual printers:

To edit a default setting, double-click in the implicit second column (wide area to the right of the preference names before the pencil button) or click the edit button. After making changes, press Enter to save your change, or click the blue checkmark button.

To modify a setting for a particular printer (for example, print.printer_Mozilla_Save_to_PDF.print_headerleft), you have two choices:

(A) To have Firefox use the default setting, delete the current custom setting using the trash can at the right end of the row for the custom setting.

(B) Edit the custom setting as desired.

Footers

(3) In the search box in the page, type or paste print_f and pause while the list is filtered

As with headers, the following three preferences are the default, but any printer-specific value overrides them, allowing you to customize individual printers:

Edits work the same way for footers as they do for headers.

Roll Back Printing Changes

This preference may be removed in the future once everything is fully debugged, but it's still available for now:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste tab_mo and pause while the list is filtered

(3) Double-click the print.tab_modal.enabled preference to switch between the new experience (true) and the classic experience (false)

(4) If there is another preference named app.normandy.startupRolloutPrefs.print.tab_modal.enabled you can double-click that one to switch it to false as well. If you do not have that one, no need to create it.

Since you are setting to false, it will look roughly like this: